Some specific services for Internet of Things, such as real-time map and providing local weather information, depend strongly on geographical time and location. We refer to the data for such service as spatio-temporal data (STD). When STD is used in a query response system similar to conventional Internet services, users not only need to acquire data actively as required, they must also have functions for retrieving data available STD. Therefore, we propose an STD retention system that uses vehicles as information hubs (InfoHubs) for disseminating and retaining the data in a specific area. In our system, InfoHubs diffuse, maintain, and advertise STD over places and times where the STD are strongly dependent, thereby allowing users to receive such data passively within the specific area. Additionally, because STD are associated with a particular space, the system can reduce search costs. We also propose an adaptive transmission control method that each vehicle effectively operates its wireless resources autonomously and STD are retained and distributed efficiently. Finally, we evaluated our proposed method using simulations and clarified that our proposed system is capable of achieving a coverage rate of nearly 100% for STD while reducing the number of data transmissions compared to existing systems.

Vehicular ad hoc networks (VANETs) are designed to provide traffic safety by enabling vehicles to broadcast information-such as speed, location and heading-through inter-vehicular communications to proactively avoid collisions. However, one powerful threat against VANETs is vehicular botnets. In our earlier work, we demonstrated several powerful vehicular botnet attacks that can have damaging impacts on the security and privacy of VANETs. In this paper, we present RIoT-the first attack in the literature against Internet of Things (IoT) devices using vehicles-and demonstrate that vehicular botnets are threats not only to VANETs, but also to other important systems and networks. We show via simulation that RIoT can compromise up to 87 percent of the IoT devices in an area of interest within a short amount of time, by taking advantage of the mobility and collective communication range of vehicular bots.

Ever growing mobile users, devices and applications lead to tremendous volume of mobile network traffic nowadays. Current cellular network infrastructure is facing the problem of lacking sufficient bandwidth. Many existing works propose to solve this issue by offloading mobile traffic to wireless local area network. However, traditional single path communications limit the traffic offloading performance due to the network handoff caused by user mobility. To further explore the benefits and potential of traffic offloading in heterogeneous mobile networks, we develop a software-defined and multipath-based network aggregation system specifically for LTE-WiFi traffic offloading in this paper. Our system relies on Multipath TCP and Software-Defined Networking technologies: the former is run on mobile devices to create TCP subflows over multiple network connections, while the latter is leveraged to direct those subflows for proper usage of network bandwidth via a centralized controller. To obtain the appropriate bandwidth allocation, we formulate traffic offloading as a network optimization problem. Furthermore, the controller configures the rate of subflows in each radio access network to optimize the objective of load balancing and fairness. The devised controller is also responsive to network status change, and the centralized design facilitates network resource management and policy making. A prototype of our traffic offloading system is implemented using network emulator Mininet-WiFi. Emulation results prove its efficiency in throughput maximization, fairness, and service continuity in heterogeneous LTE-WiFi networks.

In the era of 5G networks, smaller cell infrastructure with denser deployment of various kinds of base stations is leading the trend of the new generation of cellular networks. Benefits, such as higher throughput and lower latency, are driving people to perform further investigation and optimization while the energy efficiency aspect in 5G lacks enough attention. To enhance the energy efficiency of 5G and provide a green future cellular networks, we propose solutions to reduce the impact caused by several foreseen energy problems. We consider three scenarios from connection, communication and power perspectives, trying to minimize the energy consumption by either enforcing idle base stations to sleep or dynamically adjusting the signal range of base stations via software defined networking. Detailed discussion about scenarios and proposed solutions are presented though the simulation and evaluation are still on-going. More results will be presented in the near future.

As the Internet of Vehicles matures and acquires its social flavor, novel wireless connectivity enablers are being demanded for reliable data transfer in high-rate applications. The recently ratified New Radio communications technology operates in millimeter-wave (mmWave) spectrum bands and offers sufficient capacity for bandwidth-hungry services. However, seamless operation over mmWave is difficult to maintain on the move, since such extremely high frequency radio links are susceptible to unexpected blockage by various obstacles, including vehicle bodies. As a result, proactive mode selection, that is, migration from infrastructure- to vehicle-based connections and back, is becoming vital to avoid blockage situations. Fortunately, the very social structure of interactions between the neighboring smart cars and their passengers may be leveraged to improve session continuity by relaying data via proximate vehicles. This paper conceptualizes the socially inspired relaying scenarios, conducts underlying mathematical analysis, continues with a detailed 3-D modeling to facilitate proactive mode selection, and concludes by discussing a practical prototype of a vehicular mmWave platform.

Public cloud offers economy of scale to adapt workload changes in an autonomic manner, maximizing the use of resources. Through network function virtualization (NFV), network operators can move LTE core to the cloud; hence removing their dependency on carrier-grade LTE network functions. Recent research efforts discuss performance, latency, and fault tolerance of LTE NFV, largely ignoring the security aspects. In this paper, we discover new vulnerabilities that LTE NFV face today with no standard solutions to address them. These vulnerabilities span at both LTE control and user planes. To address them, we propose vEPC-sec that cryptographically secures LTE control-plane signaling messages in the cloud. It provides distributed key management and key derivation schemes to derive shared-symmetric keys for securing the communication between any two network functions. Our approach provides encryption and integrity protection to the messages even during virtual machines scalability and failure recovery scenarios. vEPC-sec also prevents user-plane vulnerabilities by ensuring that LTE routing modules should faithfully forward the LTE subscriber packets.

To facilitate local production and consumption (LPAC) of spatio-temporal data (STD) generated by Internet of Things (IoT) devices, we propose a STD retention system that works in collaboration with Mobile Edge Computing (MEC) infrastructure. In this paper, we will introduce the architecture of our proposed system and discuss its contributions and challenges.

A proof-of-work blockchain adopts an incentive-driven design to encourage people to participate in the network. Miners provide computing resources and services in exchange for incentives such as static block rewards and transaction fees collected from blockchain users. However, our findings suggest that the current reward scheme may not encourage miners to process user transactions. A non-cooperative strategy that submits a block with no transaction can be more rewarded than a cooperative strategy. As a consequence, the non-cooperative strategy can prevail over the cooperative strategy, decrease the system throughput, and distort credit distribution. We particularly choose Ethereum project as a subject since it is a general-purpose smart contract platform. By investigating the past two years of its ledger history, we find network propagation and block processing delays are the most significant factors that cause miners to choose the non-cooperative strategy. From this finding, we develop a more accurate statistical model for a block discovery time, as well as a reward matrix. We then derive the condition that either strategy has no additional gain, which also helps to estimate whether the transaction fee is underpriced or not. Simulation results show that the non-cooperative strategy is no longer dominant under the revised reward scheme.

The Internet became the primary medium for content sharing, playing a central role in our modern lives. This new paradigm changed the behavior of the user and the characteristics of the applications, such as multimedia content, real time interaction, among others. Thus, the Internet Service Providers (ISPs) need to evolve, adding new technologies and management strategies to their network infrastructures, resulting in the Future Internet Service Providers (FISPs). Within this context, this paper presents the key technical trends and challenges for the management of FISPs, considering the requirements of user's applications and the technologies to be standardized. Additionally, we introduce an architectural framework, called Framework for Integrated Management of Future Internet Service Providers (FIM), to expand the key technologies and to address the challenges in both access and edge networks, and to integrate the management of the FISP. A case study is presented to show the suitability of the proposed framework to enhance the management capacity of FISPs.

Many recent advances of network caching focus on i) more effectively modeling the preferences of a regional user group to different web contents, and ii) reducing the cost of content delivery by storing the most popular contents in regional caches. However, the context under which the users interact with the network system usually causes tremendous variations in a user group's preferences on the contents. To effectively leverage such contextual information for more efficient network caching, we propose a novel mechanism to incorporate context-aware collaborative filtering into demand-driven caching. By differentiating the characterization of user interests based on a priori contexts, our approach seeks to enhance the cache performance with a more dynamic and fine-grained cache allocation process. In particular, our approach is general and adapts to various types of context information. Our evaluation shows that this new approach significantly outperforms previous non-demand-driven caching strategies by offering much higher cached content rate, especially when utilizing the contextual information.

In mobile social networks, the success of resource sharing depends on a high level of cooperations. The motivation of this work is to seek conditions under which cooperation prevails without additional incentive mechanisms such as credit and reputation-based schemes. We apply the Evolutionary Game Theory framework to investigate the formation of cooperation in opportunistic resource sharing. First, we extend the existing Small World In Motion mobility model to preserve real-world localized mobility patterns. On top of the mobility model, a game theoretic model tailored for resource sharing is developed. Preliminary simulation results show that high user cooperation rate emerges when the cost of resource sharing is sufficiently small, even if the Nash Equilibrium of the resource sharing game is non-cooperation. Moreover, we discovered that heterogeneous user mobility patterns promote cooperation.

Delay Tolerant Network (DTN) routing protocols have been studied by many researchers for areas that are densely populated but have no Internet access. Many researchers have studied and proposed DTN protocols that rely on social metrics such as individual encountering frequency or centrality of a node. In this paper, we propose a DTN routing protocol, Hitchhiker, that utilizes the power of the dense crowd. Hitchhiker uses a distributed method of (i) self-clustering of mobile nodes, (ii) disseminating a packet within a local wireless subnetwork to find its intended destination, and (iii) relaying the message to the border nodes to reach the destination. We use real world human trace from two social media platforms, Twitter and Instagram, to emulate people's movement in the simulation. We find that Hitchhiker exhibits a success rate of delivery comparable to other popular DTN protocols, and also achieves sufficiently low network overhead.

Current mobile devices may reach the Internet via their multiple interfaces, i.e., WiFi and LTE. MPTCP is an ideal candidate to leverage these interfaces and make the network connectivity more robust. However, priority is given to battery conservation and turning off an energy consuming interface such as LTE while WiFi coverage is available is often the case. Even though MPTCP handles well under such conditions, it is vulnerable to handovers onto poorly performing new paths. In those scenarios, an MPTCP would be better off if the handover would not have occurred. In this paper we propose a proactive measurement of newly discovered paths as MPTCP hands over. Our algorithms leverage CapProbe to estimate the capacity in the new path and qualify its performance. We identify two metrics based on CapProbe partial measurements that declare the viability of a path to continue with the handover or revert back to the backup interface. We study our metrics and algorithm under a small test bed and real situations and show cases of MPTCP connections recovering from failed handovers.

Network functions virtualization (NFV) allows service providers to deliver new services to their customers more quickly by adopting software-centric network functions implementation over commercial, off-the-shelf hardwares. This NFV-based software-centric approach cannot use dedicated mechanisms implemented over custom built boxes to reduce latencies and tolerate faults. We present a case study of IP multimedia subsystem (IMS), which is the most complex NFV instance, requires extremely low end-to-end latency (40 msec), and demands system availability as high as five nines. Through an empirical study, we discover that highly modular IMS network functions implementation over virtualized platform: 1) incurs latencies and 2) does not tolerate faults. NFV-based IMS modules incur high latencies by creating a feedback loop among each other while executing delay sensitive data-plane traffic. These IMS modules are also susceptible to failure, causing the control-plane to terminate the application session while keeping the data-plane to forward data packets. To address these issues, we propose to refactor network function modules. We reduce latencies by pipelining the IMS modules, and recover failed modules by reconfiguring their neighboring modules. We build our system prototype of open source IMS over OpenStack platform. Our results show that our scheme reduces latencies and failure recovery time up to 12× and 10×, respectively, when compared with the state-of-the-art virtualized IMS implementation.

Reliable safety message dissemination is a fundamental primitive for constructing intersection safety systems. Normally, the dissemination is based on vehicular communications, of which the de-facto standard is Dedicated Short Range Communications (DSRC). However, due to high frequency operations, a DSRC signal is seriously attenuated when being propagated in Non Line-Of-Sight (NLOS) conditions. Previous schemes leveraged the use of centralized infrastructures or relay vehicles enabling a safety message to bypass large obstacles. However, implementing the infrastructures in all intersections would be very costly; one may not find proper relay vehicles in low density, and frequent rebroadcasts cause serious network congestion in high density. To address this challenge, we propose a novel scheme that exploits excellent propagation characteristics of a TV White Space (TVWS) band (in addition to a DSRC band) for reliable dissemination in NLOS intersections. To ensure reliable dissemination throughout a broad range of densities without infrastructures, our scheme employs two innovative mechanisms: a collaborative procedure and a Dynamic optimal Configuration (DoC). To our knowledge, this is the first that simultaneously satisfies two vital demands for intersection safety system: 1) lacking infrastructures and 2) working well in all densities. Simulation studies show that the proposed scheme outperforms previous infrastructure-based schemes.

Vehicular Ad Hoc Networks (VANETs) allow users, services, and vehicles to share information and will change our life experience with new autonomous driving applications. Multimedia will be one of the core services in VANETs and are becoming a reality in smart environments, ranging from safety and security traffic warnings to live entertainment and advertisement videos. However, VANETs have a dynamic network topology with short contact time, which leads to communication flaws and delays, increasing packet loss, and decreasing the Quality of Experience (QoE) of transmitted videos. To cope with this, neighbor vehicles moving on the same direction and wishing to cooperate should form a platoon, where platoon members act as a relay node to forward video packets in autonomous VANETs. In this article, we introduce a game theory approach for platoon‐based driving (GT4P) for video dissemination services in urban and highway VANET scenarios. GT4P encourages the cooperation between neighbor vehicles by offering reward (e.g., money or coupon) for vehicles participating in the platoon. In this sense, GT4P establishes a platoon by taking into account vehicle direction, speed, distance, link quality, and travel path, which reduces the impact of vehicle mobility on the video transmission. Simulation results confirm the efficiency of GT4P for ensuring video transmissions with high QoE support compared to existing platoon‐based driving protocols.

Vehicular ad hoc networks (VANETs) are designed to provide traffic safety by exploiting the inter-vehicular communications. Vehicles build awareness of traffic in their surroundings using information broadcast by other vehicles, such as speed, location and heading, to proactively avoid collisions. The effectiveness of these VANET traffic safety applications is particularly dependent on the accuracy of the location information advertised by each vehicle. Therefore, traffic safety can be compromised when Sybil attackers maliciously advertise false locations or other inaccurate GPS readings are sent. The most effective way to detect a Sybil attack or correct the noise in the GPS readings is localizing vehicles based on the physical features of their transmission signals. The current localization techniques either are designed for networks where the nodes are immobile or suffer from inaccuracy in high-interference environments. In this paper, we present a RSSI-based localization technique that uses mobile nodes for localizing another mobile node and adjusts itself based on the heterogeneous interference levels in the environment. We show via simulation that our localization mechanism is more accurate than the other mechanisms and more resistant to environments with high interference and mobility.

Sybil attacks are a challenging security threat in ad-hoc and vehicular networks. A malicious node can successfully launch a Sybil attack with high probability. However, the targeted node has difficulty in discriminating whether the neighboring node is a Sybil or an honest node. Furthermore, Sybil attacks may have the grave consequence of compromising network reliability. To this end, we propose a novel method to effectively detect and thwart Sybil attacks through electro-acoustic positioning with context-aware information. By using electro-acoustic positioning, each node accurately verifies nearby Sybil identities, and shares the verified node information with others. As a result, our proposed scheme allows small pieces of information to form a complete picture of the Sybil node distribution. Our extensive simulation results show that our approach outperforms existing solutions in detection of Sybil attacks and provides better accuracy even in relatively sparse networks.

Vehicular Ad-hoc NETworks (VANETs) promise a wide scope of multimedia services ranging from security and traffic announcements to entertainment and advertising videos. However, VANETs have a dynamic network topology with short contact time, decreasing the Quality of Experience (QoE) of transmitted videos due to frequent disconnections in the communication between neighbours vehicle. Those disconnections cause communication flaws and delays, increasing the packet loss during video transmissions. To cope with this, neighbor vehicles moving on the same direction and wishing to cooperate could form a platoon to disseminate live videos. In this paper, we introduce a platoon protocol based on game theory for video dissemination with QoE support, called P2V. The proposed protocol provides cooperation between neighbor vehicles to establish a platoon by taking into account vehicles direction, speed, and distance, where P2V provides a reward (money or coupon) for vehicles participating in the platoon. Simulation results confirm the efficiency of the P2V protocol to ensure video transmission with high QoE support compared to BLR and XLinGO protocols.

In the Intelligent Vehicle Grid, the car is becoming a formidable sensor platform, absorbing information from the environment, from other cars (and from the driver) and feeding it to other cars and infrastructure to assist in safe navigation, pollution control and traffic management. The Vehicle Grid essentially becomes an Internet of Things (IOT), which we call Internet of Vehicles (IOV), capable to make its own decisions about driving customers to their destinations. Like other important IOT examples (e.g., smart buildings), the Internet of Vehicles will not merely upload data to the Internet using V2I. It will also use V2V communications between peers to complement on board sensor inputs and provide safe and efficient navigation. In this paper, we first describe several vehicular applications that leverage V2V and V2I. Communications with infrastructure and with other vehicles, however, can create privacy and security violations. In the second part of the paper we address these issues and more specifically focus on the need to guarantee location privacy to mobile users. We argue on the importance of creating public, open "smart city" data repositories for the research community and propose privacy preserving techniques for the anonymous uploading of urban sensor data from vehicles.

LTE Network Function Virtualization (LTE-NFV) scales user services in a low cost fashion by transforming the centralized legacy LTE Core architecture to a distributed architecture. This distributed architecture makes multiple instances of LTE Network Functions (NFs) and virtualizes them on commodity data-center network. The functionality of LTE-NFV architecture breaks however, since the distributed NF instances connected via unreliable IP links delay the execution of critical events. The failure of time-critical events results in users' quality of service degradation and temporary service unavailability. In this paper, we propose a new way to virtualize LTE core network. We argue that logic-based NFs segregation should be done for NFV, instead of instance-based NFs segregation done in current NFV implementation. Our approach of ‘logic-based NFs segregation’ combines the logic of an event into a single NF, thus localizing the execution of critical events to one virtual machine. This way, only the localized entities exchange signalling messages, and the events do not experience large delays. We further reduce the delays by exploiting the parallelism in LTE network protocols; and partition these protocols such that their signalling messages run in parallel. In addition, we eliminate unnecessary messages to reduce the signalling overhead. We build our system prototype over OpenEPC LTE core network in virtualized platform. Our results show that we can reduce event execution time and signalling overhead up to 50% and 40%, respectively.

Network coding can significantly enhance reliability and throughput in wireless networks. However, network coding comes with a considerable cost in terms of computing, storage, and power consumption. In this paper, we propose a constraint-aware distributed algorithm which considers the contribution of each node in generating coded packets and opportunistically makes use of multiple available paths to forward unicast traffic while providing a reliable data delivery. We demonstrate the effect of the scheme, particularly in terms of overhead, through simulation in different network topologies.

Delay-tolerant networks (DTN) are sparse mobile ad hoc networks where contemporaneous end-to-end path is typically not available. Therefore, nodes act as relays for each other to enable data delivery. The cooperation among mobile nodes however can be hindered by selfish users. Incentive schemes are inevitably introduced to regulate the behavior of DTN users. The motivation of this paper is to seek conditions under which cooperators can survive, and even prevail in DTN without incentives. We study the formation of cooperation in DTN routing following an Evolutionary Game Theory (EGT) approach. In particular, the two-hop routing protocol is assumed to be adopted which applies to a large class of DTN routing schemes. We first formulate the two-hop DTN routing as a multi-player game. Using the concept of Evolutionarily Stable Strategy (ESS), we show that defection always dominates cooperation when the population is infinite and well-mixed. Recent developments in evolutionary biology reveal that in finite and structured populations such as graphs, cooperation is nevertheless promoted. We derive a sufficient condition for cooperators to be favored over defectors on K-regular graph. Simulation results validate our theoretical finding, and prove that cooperation indeed can prevail in DTN routing games without incentives.

Delay Tolerant Networks (DTNs) are sparse mobile ad-hoc networks in which there is typically no complete path between the source and destination. Although many routing algorithms for DTNs have been proposed, prior works generally focus on utilizing the delivery probability of network nodes and the social network structure for data forwarding. In this work, we investigate the use of the inter-contact time (ICT) distribution to derive a new metric that selects the next relay node with the least expected minimum delay (EMD) among all possible routes to the destination. We address the case of exponential and power-law ICTs, which are the most popular assumptions for ICTs that have emerged in recent literature. Extensive simulation results based on the Cabspotting and Cambridge Haggle traces show that our proposed metric can achieve up to 21% higher delivery rate and 23% lower delay than existing schemes.

Summary form only give, as follows. Provides an abstract of the keynote presentation and a brief professional biography of the presenter. The complete presentation was not made available for publication as part of the conference proceedings. Traditionally, the vehicle has been the extension of the man's ambulatory system, docile to the driver's commands. Recent advances in communications, controls and embedded systems have changed this model, paving the way to the Intelligent Vehicle Grid. The car is now a formidable sensor platform, absorbing information from the environment, from other cars (and from the driver) and feeding it to other cars and infrastructure to assist in safe navigation, pollution control and traffic management. The next step in this evolution is just around the corner: the Internet of Autonomous Vehicles. Pioneered by the Google car, the Internet of Vehicles will be a distributed transport fabric capable to make its own decisions about driving customers to their destinations. Like other important instantiations of the Internet of Things (e.g., the smart building), the Internet of Vehicles will not merely upload data to the Internet. It will have its own communications, storage, intelligence, and learning capabilities to anticipate the customers' intentions. The concept that will help transition to the Internet of Vehicles is the Vehicular Cloud, the equivalent of Internet cloud for vehicles, providing the basic services required by the autonomous vehicles. This talk will trace the evolution from Intelligent Vehicle Grid to Autonomous, Internet-connected Vehicles, and Vehicular Cloud.

Delay Tolerant Networks (DTNs) are sparse mobile ad-hoc networks in which there is typically no complete path between the source and destination. While much work has been done in the design of forwarding algorithms, little work has focused on studying forwarding under the presence of short contact durations. In this paper, we study a single- copy contact duration-aware (CDA) routing strategy. We address two key issues: (1) to which next hop relay node should messages be forwarded and (2) in which order should messages be forwarded. To reduce the transmission cost, we select relay nodes from both current and past contacts based on the one-hop and two-hop delivery probability, respectively. We derive the delivery probability from the distribution of contact duration time and inter- contact time. For the message scheduling, messages with the highest delivery probability are prioritized to be transmitted first. Extensive simulation results based on the Cabspotting trace show that our scheme can achieve up to 13% higher delivery rate, 12% lower delay, and 23% lower transmission cost compared to other routing strategies.

We consider the problem of routing in a mobile ad-hoc network (MANET) for which the planned mobilities of the nodes are partially known a priori and the nodes travel in groups. This situation arises commonly in military and emergency response scenarios. Optimal routes are computed using the most reliable path principle in which the negative logarithm of a node pair's adjacency probability is used as a link weight metric. This probability is estimated using the mobility plan as well as dynamic information captured by table exchanges, including a measure of the social tie strength between nodes. The latter information is useful when nodes deviate from their plans or when the plans are inaccurate. We compare the proposed routing algorithm with the commonly-used optimized link state routing (OLSR) protocol in ns-3 simulations. As the OLSR protocol does not exploit the mobility plans, it relies on link state determination which suffers with increasing mobility. Our simulations show considerably better throughput performance with the proposed approach as compared with OLSR at the expense of increased overhead. However, in the high-throughput regime, the proposed approach outperforms OLSR in terms of both throughput and overhead.

Given that the exact answer to a question is fixed, we ask is it possible to strengthen the privacy by increasing the crowd size that participates even though they do not contribute to the exact answer? In this paper, we introduce the notion of scalable privacy whereby data owners not at a particular location privatize their response such that they respond as if they are at a location (even when they are not). Immediately the question of utility is raised and we examine the tradeoffs to construct such a privacy mechanism so that it scales in both privacy and utility.

In this paper we introduce the concept of CrowdZen Privacy. CrowdZen Privacy privately publishes the activity levels of places of interest (e.g., dining halls, libraries, gyms) and leverages the randomness of the crowd and variance of the estimation to satisfy differential privacy while preserving accuracy. We define the CrowdZen privacy mechanism and have implemented the system on iOS and Android mobile devices.

Autonomic communications aim to provide the quality-of-service in networks using self-management mechanisms. It inherits many characteristics from autonomic computing, in particular, when communication systems are running as specialized applications in software-defined networking (SDN) and network function virtualization (NFV)-enabled cloud environments. This paper surveys autonomic computing and communications in the context of software-driven networks, i.e., networks based on SDN/NFV concepts. Autonomic communications create new challenges in terms of security, operations, and business support. We discuss several goals, research challenges, and development issues on self-management mechanisms and architectures in software-driven networks. This paper covers multiple perspectives of autonomic communications in software-driven networks, such as automatic testing, integration, and deployment of network functions. We also focus on self-management and optimization, which make use of machine learning techniques.

The performance of mobile ad hoc network transmissions subject to disruption, loss, interference, and jamming can be significantly improved with the use of network coding (NC). However, NC requires extra work for forwarders, including additional bandwidth consumption due to transmitting overheads for redundant NC packets and additional processing due to generating the NC packets. Selfish forwarders may prefer to simply forward packets without coding them to avoid such overhead. This is especially true when network coding must be protected from pollution attacks, which involves additional, often processor intensive, pollution detection procedures. To drive selfish nodes to cooperate and encode the packets, this paper introduces social norm-based incentives. The social norm consists of a social strategy and a reputation system with reward and punishment connected with node behavior. Packet coding and forwarding are modeled and formalized as a repeated NC forwarding game. The conditions for the sustainability (or compliance) of the social norm are identified, and a sustainable social norm that maximizes the social utility is designed via selecting the optimal design parameters, including the social strategy, reputation threshold, reputation update frequency, and the generation size of network coding. For this game, the impacts of packet loss rate and transmission patterns on performance are evaluated, and their impacts on the decision of selecting the optimal social norm are discussed. Finally, practical issues, including distributed reputation dissemination and the existence of altruistic and malicious users, are discussed.

Named Data Networking (NDN) has been recently added to the future Internet family. NDN is basically an extension to the Content Centric Network (CCN) and is expected to support various applications. Those applications are to be supported by the future internet architectures. NDN believes in naming the content rather than using end-to-end device names. Recently, NDN has been adapted into Vehicular Ad hoc Networks (VANETs) and hence, we name it Vehicular NDN (VNDN). At it's early stage, VNDN faces several challenges such as consumer/provider mobility, Interest/Data forwarding, content caching and so on. Mostly, VNDN relies on the fact that Data is sent back to the consumer via same path the Interest packet was received from. However, we analyzed that it's not true in a VANET and there is lack of discussion about managing the Data flow back to the consumers in the current literature of VNDN. In this paper, we therefore, pursue to control the data flooding/broadcast storm of the conventional VNDN by proposing our scheme “CONET”. The main idea of CONET is to allow the consumer vehicle to start hop counter in the Interest message and upon receiving that interest by any potential provider, to include Time To Live (TTL) value with data messages. The TTL value includes the number of hops, Data packets should travel on its way back to the consumer. Simulation results show that CONET forwards less Copies of Data Messages Processed (CDMP) while achieving similar Interest Satisfaction Rate (ISR) as the basic VNDN. In addition, CONET also minimizes the overall Interest Satisfaction Delay (ISD), respectively.

Even after decades, the Internet does not provide Quality of Service (QoS) guarantee for the users. In order to soften such situation, clients negotiate Service Level Agreements (SLAs) with their Internet Service Providers (ISPs), where reliability and available bandwidth are key requirements for Internet services. On the other hand, the ISPs aim to decrease the energy consumption to deliver their services and provide a green environment. The mixing of Software Defined Networks (SDNs) and Virtual Networks (VNs), called Virtual Software Defined Network (VSDN), arises as a realizable option to deal with both client and provider perspectives. Within this context, this paper proposes two algorithms to allocate VSDNs combining reliability, bandwidth, and energy efficiency, considering the current network state to adjust the importance of each of these aspects during the allocation process. The results show the effectiveness of the proposed algorithms in allocating reliable VSDNs, while improving the energy efficiency and bandwidth usage of the ISP.

Quorum-based schemes have been receiving much attention since they can efficiently provide the Sink Location Service (SLS) with large-scale networks and lightweight sensor nodes. Recently, researchers try to adopt them to real irregular fields with voids as well as non-rectangular shapes. However, such schemes make quorums only on particular path such as boundary or selected circle, thus leading to rapid energy exhaustion of nodes on the path. In this paper, we propose an energy-balanced SLS scheme. By constructing a quadrangle quorum per each sink connected by four random points, the scheme costs a balanced energy consumption of nodes, thus can prolong the network lifetime.

With technology advancement, Vehicular Ad Hoc Networks (VANETs) have been requested to provide one-to-many group communications (i.e. multicasting) for business and entertainment applications such as video conferences and file sharings. For these group communication applications, the existing broadcasting-based and unicasting-based approaches designed for safety applications however cause high packet generations and redundant data transmissions, respectively. Although the well-known Shortest Path Tree (SPT) and Minimum Spanning Tree (MST) algorithms for multicasting have been proposed, they achieve only a specific goal such as the reduction of delay or tree cost. Thus, for reducing end-to-end delay, delay variation, and transmission number requested for delay-sensitive and cost-efficient group communications and supporting high mobility of vehicles, this paper proposes a multicast protocol which uses the Farthest destination Selection and Shortest path Connection (FSSC) strategy to form a multicast tree. FSSC relies on the road map information and the location information of vehicles and intersections. Simulation results are provided to verify the effectiveness of FSSC.

Communications for mobile sink groups such as rescue teams or platoons bring about a new challenging issue for handling mobility in wireless sensor networks. Recently, a group region-based approach has been proposed to send data to a mobile sink group. However, it uses flooding for discovering and notifying group region information and flooding or long distance forwarding for disseminating data. Thus, it causes high energy consumption and data delivery failure. Moreover, its per-sink mobility supporting scheme makes energy consumption and data delivery failure more serious. Thus, this letter proposes an Energy-efficient and Reliable Mobile Group communication protocol (ERMG) to support a mobile sink group, which exploits a virtual grid structure. For the group region discover and notification and the data dissemination, ERMG uses communications with only cell heads of grid cells that manages group sinks. ERMG also uses a per-grid based scheme to support sink mobility. Simulation results show that ERMG has better performance than the existing protocols.

In Delay Tolerant Networks (DTNs) with resource constraints such as short contact durations and small buffers, message scheduling and drop prioritization is a critical issue as it affects the routing performance. Current solutions mainly focus on devising buffer management strategies by assuming that the contact rates between mobile nodes are exponentially distributed. While this assumption is suitable for vehicular mobility scenarios such as taxicabs in a city, it is often invalid for mobility traces that feature human-assisted devices. Recent studies have shown that human mobility traces follow a truncated power-law distribution. In this paper, we propose a new buffer management strategy based on power-law distributed contacts. The main objective is to minimize the average message delivery delay in DTN networks with resource constraints and heterogeneous node mobility. We focus on two key issues: (1) in which order should messages be replicated when contact duration and forwarding bandwidth are limited, and (2) which messages should be dropped first when the buffer is full. We develop a utility function using global network information to compute per-packet average delay utility. Messages are then scheduled and dropped according to their utility values. Extensive simulation results based on real-life human mobility traces show that our proposed scheme can deliver messages in up to 27% less time than existing schemes, while still achieving a high delivery ratio.

Vehicular ad hoc networks (VANETs) are expected to play a big role in our lives in the near future; they will both improve traffic safety and revolutionize the driving experience. Their expected deployment in autonomous cars will induce attackers to design new methods to target these systems, and to organize the vehicles they compromise into vehicular botnets. Vehicular botnets enable new attacks that reveal previously unknown security flaws in VANETs. Effectively defending against such botnets requires investigation of their characteristics and of the attacks that these cooperating malicious vehicles can perform on VANETs. One important characteristic of a botnet is the way its members communicate to coordinate their attacks, with an emphasis on stealth. In this paper, we investigate alternatives for vehicular botnets to communicate to perform attacks. We design and demonstrate a VANET-based botnet communication protocol that hides itself in the ongoing network traffic over the control channel. We show via simulation that it is infeasible to detect such botnet communications due to the vulnerabilities existing in the VANET standards, and discuss possible countermeasures.

In this paper, we address several security issues in our previously proposed content retrieval scheme for Disruption Tolerant Networks (DTNs). The content retrieval is built upon the social-tie relationships among DTN nodes for routing and content lookup service placement. Malicious nodes can launch attacks by advertising falsified social-tie information to attract and drop packets intended for other nodes, or simply disrupt and destroy the query and delivery paths. Furthermore, selfish nodes, while not seeking to attack, are unwilling to forward packets of others. Both malicious and selfish behaviors contribute to the deterioration of the content retrieval performance. To address the problem, we propose to secure both social-tie records and content delivery records during a contact between two nodes. The unforgeable social-tie records prevent malicious nodes from falsifying the social-tie information. The delivery records from which the packet forwarding ratio of a node is computed, help detect selfish behavior. Lastly, we propose a blacklist distribution method that allows nodes to filter out misbehaving nodes from their social contact graph, effectively preventing network traffic from flowing to misbehaving nodes. Extensive real-trace-driven simulation results show that our scheme can detect misbehaving nodes and mitigate their effects efficiently, thus improving the content retrieval performance.

The research on mobile groupcasting has been studied to deliver messages of interests to all mobile sinks that have collective mobility as a group. It provides a current geographical region of the group to a data source to support mobile sink groups in a macroscopic view of the group mobility. Several protocols have been proposed for mobile groupcasting and can be classified into two data dissemination strategies: unicasting and flooding. In aspects of energy efficiency, unicasting is good for a small number of sparse sinks, while flooding is good for a large number of dense sinks. However, since both extremes are too conservative, they are hard to support the generic case that the region is overall sparse and partially dense. In this paper, we suggests an energy-efficient mobile groupcasting protocol, which exploits both unicasting for sparse sinks and partial flooding for dense sinks in a group region. To do this, we present an analytical model to calculate an optimal combination of both a flooding subgroup for the sparse sinks and an unicasting subgroup for the dense sinks. By separating a group into a unicasting subgroup and a flooding subgroup, the proposed protocol can efficiently eliminate unnecessary flooding areas as well as duplicated transmissions. Simulation results in various environments shows that the proposed protocol has better performance than the existing protocols.

Network coding can significantly enhance throughput and reliability in loss prone wireless networks. Adapting network coding redundancy is critical, since over-redundancy wastes network resources and hurts performance and under-estimated redundancy prevents decoding at destination. In this paper, we study the tradeoff between application tolerated loss rate and network overhead introduced by network coding redundancy. We first propose an analytic model that determines a simple redundancy bound to adapt network coding redundancy according to the measured packet loss rate and the targeted maximum application loss rate. Then, we propose a distributed algorithm with adaptive redundancy for reliable data delivery in wireless meshes. In the algorithm, each node opportunistically makes use of multiple paths available in the network to deliver data to the destination. We demonstrate the benefits of our schemes through simulation in various network scenarios.

We study a network utility maximization (NUM) decomposition in which the set of flow rates is grouped by source-destination pairs. We develop theorems for both single-path and multipath cases, which relate an arbitrary NUM problem involving all flow rates to a simpler problem involving only the aggregate rates for each source-destination pair. The optimal aggregate flows are then apportioned among the constituent flows of each pair. This apportionment is simple for the case of a-fair utility functions. We also show how the decomposition can be implemented with the alternating direction method of multipliers (ADMM) algorithm.

Due to the unstable network topology of Delay Tolerant Networks (DTNs), multi-copy routing is often used to increase the reliability of message delivery. However, this routing approach suffers from high buffer and bandwidth overhead. While much work has been done in the design of forwarding algorithms, little work has focused on studying forwarding under the presence of resource constraints such as short contact durations and small buffers. In this paper, we investigate a multi-copy routing strategy and a buffer management policy that maximize the delivery rate in DTNs. We consider a realistic DTN environment with resource constraints, heterogeneous node mobility, and varied message sizes. There are three key issues in DTN routing: (1) to which next hop relay node should messages be replicated, (2) in which order should messages be replicated, and (3) which messages should be dropped first when the buffer is full. We propose to forward a message to a neighboring node that has both a stronger social tie with the destination and a smaller or similar queue length. This aims to reduce traffic at highly connected network nodes, avoiding frequent message drops which compromise the delivery ratio. For the second and third issue, we develop a utility function using global network information to compute per-packet delivery rate utility. Messages are then scheduled and dropped according to their utility values. Extensive simulation results based on the real-world San Francisco cab trace show that our proposed scheme can achieve a delivery rate of up to 22% higher than existing schemes, while still maintaining a comparable average delivery delay. Furthermore, our scheme distributes the network loads more evenly, with the top 10% of network nodes handling only 24% of the forwardings.

It is a consensus that the Internet suffers from architectural limitations, including resilience, scalability, and manageability, among others. Therefore, companies access the Internet by establishing a service level agreement (SLA) in the attempt to ensure quality of service (QoS) for users. To address the current limitations of the Internet, researchers have recently proposed the edge as a service (EaaS) paradigm as a suitable solution to improve the access capacity of edge networks. EaaS uses network virtualization and software-defined networks to expand flexibility and manageability of access to edge network resources. Moreover, to maintain QoS assurance for users, EaaS addresses network events (such as traffic overload, failures, etc.) that can potentially affect QoS. Within this context, this paper proposes a software-defined management of EaaS environment, called SDM-EaaS. The proposal enhances the QoS for the end user, while improving the utilization of network resources in dynamic scenarios allowing for unpredictable changes in traffic demands, network infrastructure availability, and customer characteristics. Experiments based on emulation as well as real testbed demonstrate the effectiveness of the SDM-EaaS strategy.

Abstract This paper presents a secure communication application called DiscoverFriends. Its purpose is to securely communicate to a group of online friends while bypassing their respective social networking servers under a mobile ad hoc network environment. DiscoverFriends leverages Bloom filters and a hybrid encryption technique with a self‐organized public‐key management scheme to securely identify friends and provide authentication. Additionally, DiscoverFriends enables anonymous location check‐ins by utilizing a new cryptographic primitive called function secret sharing. Finally, to the best of our knowledge, DiscoverFriends implements and evaluates the first Android multi‐hop WiFi direct protocol using IPv6. Copyright © 2016 John Wiley & Sons, Ltd.

Abstract Delay‐tolerant networks are sparse mobile ad hoc networks in which there is typically no complete path between the source and destination. Although many routing schemes for delay‐tolerant networks have been proposed, they do not address fairness issues in terms of the workload/traffic handled at each node and the share of throughput among different destination nodes. In this paper, we propose a socially aware routing strategy that optimizes both fairness and throughput. A relay node is selected based on the multi‐hop delivery probability and its queue length. The effect of queue length control is to divert traffic away from highly connected nodes and allows nodes to explore less‐congested paths to the destination. This helps balance the network loads, thus achieving workload fairness. Furthermore, to achieve throughput fairness, we sort arriving messages into different destination‐based queues. Messages are then scheduled following a two‐level forwarding strategy that optimizes throughput fairness using round‐robin and delivery ratio using priority scheduling. Extensive real‐trace‐driven simulation results show that our scheme outperforms existing algorithms in terms of the delivery ratio. Furthermore, our scheme achieves a high throughput fairness, while distributing the network loads more evenly, with the top 10% of network nodes handling only 22% of the forwardings. Copyright © 2016 John Wiley & Sons, Ltd.

In this paper we conduct a performance evaluation of privacy protocols for Information Centric Networking (ICN). Our contribution is three-fold: Firstly, we define a simple but complete performance framework for comparing current and future solutions. Secondly, we conjecture and prove the existence of unsafe replicas, namely cached content that remains available to users whose access has been revoked. Thirdly, we propose a performant protocol that solves the problem of unsafe replicas without tampering with the caching functionality of ICN.

The increasing popularity and acceptance of VANETs will make the deployment of autonomous vehicles easier and faster since the VANET will reduce dependence on expensive sensors. Many useful applications will be possible with the usage of VANETs, which will improve the safety and quality of trips for the owners of these vehicles. One of these applications is the avoidance of traffic congestion by smart dynamic rerouting. For scalability, current cloud-based solutions, like Google Maps traffic, update congestion levels after a time interval rather than providing real-time measurements. In this paper, we introduce a vehicle-to-vehicle congestion avoidance mechanism, which detects real-time congestion levels and reroutes vehicles accordingly to minimize their trip times. Our system is highly distributed and is, therefore, not subjected to the limitations of centralized congestion avoidance mechanisms. We show via simulation that our system can significantly decrease the trip times of vehicles as well as the average car density on the map. Our proposed system, with its checkpoint and offline path generation approaches, is more responsive to local congestion level changes and computationally less complex for least congested route calculations than state-of-the-art congestion avoidance mechanisms.

The Internet is now present in our personal and professional life, where reliability and green communications are still open issues to be addressed. Usually, clients establish Service Level Agreements (SLAs) with their Internet Service Providers (ISPs), including parameters of reliability and bandwidth. On the other hand, the ISPs aim to maximize their profit by establishing as many SLAs as possible and decreasing the energy consumption to provide their services. In this context, this paper presents an algorithm for Virtual Software Defined Network (VSDN) allocation that considers both reliability and energy efficiency. The algorithm deploys the VSDN aiming to comply with the parameters defined in SLAs, as well as to improve the energy efficiency of the ISP. Experiments using a real network topology show the effectiveness of the algorithm to deploy the VSDN with a performance 15% better than existing algorithms.

This paper proposes a network-aware resource management scheme that improves the quality of experience (QoE) for adaptive video streaming in CDNs and Information-Centric Networks (ICN) in general, and Dynamic Adaptive Streaming over HTTP (DASH) in particular. By utilizing the DASH manifest, the network (by way of a logically centralized controller) computes the available link resources and schedules the chunk dissemination to edge caches ahead of the end-user's requests. Our approach is optimized for multi-rate DASH videos. We implemented our resource management scheme, and demonstrated that in the scenario when network conditions evolve quickly, our approach can maintain smooth high quality playback. We show on actual video server data and in our own simulation environment that a significant reduction in peak bandwidth of 20% can be achieved using our approach.

Nowadays, the multimedia content accessed by users represents 55% of the Internet traffic and it is forecast to expand to 92% by 2020. This fact increased the resource demand in access networks across the world, since multimedia traffic has high network requirements. To deal with this scenario, Internet Service Providers (ISPs) tend to apply the Edge as a Service (EaaS) approach. EaaS aims to use Network Virtualization and Network Programmability to expand the flexibility of access to edge network resources. In this context, this paper presents the Bitrate-Aware Virtual Resources Adjustment (BEAVER) mechanism, which increases the Quality of Experience (QoE) support for multimedia clients in EaaS environments. Experiments using real traffic demonstrate the effectiveness of the proposed mechanism to ensure the user's QoE.

We study the throughput and delay scaling laws of cognitive radio networks (CRN) with mobile primary and secondary users. They operate at the same time, space and share the spectrum. The primary users (PUs) have higher priority to access the spectrum while the secondary users (SUs) should access opportunistically. Furthermore, we consider a unique situation where both PUs and SUs move according to a General Heterogeneous Speed-restricted Mobility (GHSM) model. In this model, we define (h + 1) heterogeneous moving patterns using a universal set T ={Ti|0 ≥ i ≤ h, Ai= n-iχ0/h}, where Aidetermines the moving area of each pattern. The set of primary (secondary) moving patterns T(p)(T(s)) is a randomly and independently selected subset of T. We assign n (nβ, where β > 1) primary (secondary) nodes to each moving pattern, and their initial positions are subject to a poisson point process. In addition, we have |T(p)|~|T(s)| = Θ1(h) = Θ(log n). By proposing a cooperative routing strategy, we fully utilize the mobility heterogeneity of primary and secondary users and achieve near-optimal throughput and delay performance of order Θ(poly log n) when χ0≥ β. In other cases, our transmission scheme shows advantages over [1] in delay performance of the primary network (PN) and over [2] in capacity of the secondary network (SN).

While geo-routing is a promising routing algorithm in urban vehicular ad-hoc networks (VANETs), there is still much work to be done for it to become truly usable for such environments. One of the biggest obstacles to this goal is the intermittent nature of VANETs due to mobility. Traditional geo-routing algorithms do not perform well in these conditions because they drop packets whenever they cannot find an immediate forwarder for the packet. In this paper, we propose RobustGeo, a routing protocol that combines the simplicity and efficiency of the greedy forwarding technique in geo-routing algorithms, with the robustness of delay tolerant networks in the face of disruptions in network connectivity. When there exists a good connection between the source and destination, RobustGeo can route the packet like the traditional geo-routing algorithms, and when the network faces disruptions, RobustGeo relies upon vehicle mobility and packet replication to explore multiple georoute paths and quickly recover the packet back to greedy forwarding. We show that for a highly intermittent scenario, RobustGeo has a delivery ratio of over 20% (compared to a pure geo-routing protocol's delivery ratio of 0), and it reduces delay by over 40% as compared to a more pure delay-tolerant routing solution.

Real-time video dissemination over Vehicular Ad hoc Networks (VANETs) is fundamental for many services, e.g., emergency video delivery, road-side video surveillance, and advertisement broadcasting. These applications deal with several challenges due to strict video quality level requirements and highly dynamic topologies. To handle these challenges, geographic receiver-based beacon-less approaches have been proposed as a suitable solution for forwarding video flows in VANETs. In general, the routing decisions are performed only based on network, link, and/or node characteristics, such as link quality and vehicle's location. However, in real situations, due to different requirements and hierarchical structures of multimedia applications, these existent routing decisions are not satisfactory to select the best relay nodes and build up reliable backbones to delivery video content with reduced delay and high Quality of Experience (QoE). This paper introduces the QOe-Driven and LInk-qualiTy rEceiver-based (QOALITE) protocol to allow live video dissemination with QoE assurance in Vehicle-to-Vehicle (V2V) scenarios. QOALITE considers video and QoE-awareness, coupled with location and link quality attributes for relay selection. Simulation results show the benefits of QOALITE when compared to existing work, while achieving multimedia transmission with QoE support and robustness in highway scenarios.

Neighbor discovery plays a crucial role in the formation of wireless sensor networks and mobile networks where the power of sensors (or mobile devices) is constrained. Due to the difficulty of clock synchronization, many asynchronous protocols based on wake-up scheduling have been developed over the years in order to enable timely neighbor discovery between neighboring sensors while saving energy. However, existing protocols are not fine-grained enough to support all heterogeneous battery duty cycles, which can lead to a more rapid deterioration of long-term battery health for those without support. Existing research can be broadly divided into two categories according to their neighbor-discovery techniques — the quorum based protocols and the co-primality based protocols. In this paper, we propose two neighbor discovery protocols, called Hedis and Todis, that optimize the duty cycle granularity of quorum and co-primality based protocols respectively, by enabling the finest-grained control of heterogeneous duty cycles. We compare the two optimal protocols via analytical and simulation results, which show that although the optimal co-primality based protocol (Todis) is simpler in its design, the optimal quorum based protocol (Hedis) has a better performance since it has a lower relative error rate and smaller discovery delay, while still allowing the sensor nodes to wake up at a more infrequent rate.

In wireless networks, broadcasting is a fundamental communication primitive for network management and information sharing. However, in multi-channel networks, the broadcast efficiency is very poor as devices are distributed across various channels. Thus, a sender tries all channels for broadcasting a single message, which causes large overhead. In this paper, we propose a novel scheme for efficient broadcast in multichannel networks. Our scheme leverages the overlapped band, which is the frequency range that partially overlapped channels (i.e., adjacent channels) share within their channel boundaries. Specifically, a sender advertises the rendezvous channel through the overlapped band of adjacent channels; the message sharing via broadcast is done on the rendezvous channel. Our scheme employs Signaling via Overlapped Band (SOB), which defines a new signal processing mechanism for communication via the overlapped band. SOB is integrated with MAC layer mechanisms: 1) Reserve Idle Spectrum Fragment (RISF) to reduce waiting time, 2) Reinforce Switch Notification (RSN) to reduce the residing time at a wrong channel, and 3) Multi-sender Agreement on Rendezvous CHannel (MARCH) to support multisender broadcasts. We implemented our scheme on the SORA platform. Experiment results validated communication through the overlapped band. Intensive simulation studies showed that our scheme drastically outperformed previous approach.

This paper presents a secure communication application called DiscoverFriends. Its purpose is to communicate to a group of online friends while bypassing their respective social networking servers under a mobile ad hoc network environment. DiscoverFriends leverages Bloom filters and a hybrid encryption technique with a self-organized public-key management scheme to securely identify friends and provide authentication. Firstly, Bloom filters provide a space-efficient means of security for friend discovery. Secondly, a combination of asymmetric and symmetric encryptions algorithms utilizes both benefits to provide increased security at lower computational cost. Thirdly, a self-organized public-key management scheme helps authenticate users using a trust graph in an infrastructureless setting. With the use of Wi-Fi Direct technology, an initiator is able to establish an ad hoc network where friends can connect to within the application. DiscoverFriends was analyzed under two threat models: replay attacks and eavesdropping by a common friend. Finally, the paper evaluates the application based on storage usage and processing.

Low earth orbit (LEO) satellite networks like Iridium have played a pivotal role in providing ubiquitous network access services to areas without terrestrial infrastructure because of their potential for global coverage and high bandwidth availability. With low orbit and short range as compared to geostationary satellites, LEO satellites are accessible by mobile devices with limited transmission power and small gain antennas. The drawback, however, is that LEO satellites move fast across the sky with average contact time in the order of 10 minutes, thus requiring frequent handover from one satellite to the next. To achieve smooth handover and efficiently utilize constellation capacity, we propose to use Multipath TCP (MPTCP) in LEO systems and maintain parallel, simultaneous connections between terrestrial handpoints via multiple satellites. In this paper, we discuss the feasibility of using MPTCP over LEO satellite networks and propose a framework of MPTCP-Routing design. Then the performance of this protocol is evaluated through simulation. We show that compared to traditional “single-path” TCP, MPTCP significantly improves throughput performance and prevents the interruption of transmission during handover. Furthermore, we show that our MPTCP-Routing interaction is essential for the end-to-end session to quickly recover from handover.

Delay Tolerant Networks (DTNs) are sparse mobile ad-hoc networks in which there is typically no complete path between the source and the destination. Data routing in DTNs is challenging, and has attracted much attention from the research community. Although many routing schemes have been proposed, they do not address the fairness issue in data delivery to different destination nodes. In this paper, we propose a novel socially-aware routing strategy that optimizes both fairness and throughput. We combine controlled data “spraying” at the source node and single-copy routing at the intermediate nodes. A replication decision is made based on the delivery probability computed over the most probable path in the social contact graph. Furthermore, at intermediate nodes, we sort arriving data into different queues. We then propose a two-level data forwarding strategy that optimizes fairness using round-robin at the first level and throughput using priority scheduling at the second level. Through extensive simulation studies using a real-world mobility trace, we show that our scheme achieves a high delivery ratio, low delay, and low replication overhead.

As vehicles will soon become network connected, new vehicle applications are emerging, from navigation safety to location aware content distribution, urban surveillance and intelligent transport. Autonomous vehicles stand out as important players, with plenty of sensors, memory and processing power. The richness of on-board resources and the diversity of applications set the Vehicular ad Hoc Network(VANET) apart from conventional MANETs and introduce new challenges in the services they provide. First, it becomes apparent that safe navigation in a future with autonomous car platoons, say, will demand efficient, low latency V2V. Moreover, other applications (eg, surveillance, traffic management, etc) will require a degree of coordination not possible with the conventional Internet Cloud. To this end, low latency cooperation can be best supported by a Mobile Computing Cloud (MCC), where vehicles use V2V to propagate computation results, share resources and provide mobile services. This talk will revisit VANET applications and will propose a Vehicular Cloud platform along with representative mobile service examples.

In this paper, we propose a distributed content retrieval scheme for Disruption Tolerant Networks (DTNs). Our scheme consists of two key components: a content discovery (lookup) service and a routing protocol for message delivery. Both components rely on three key social metrics: centrality, social level, and social tie. Centrality guides the placement of the content lookup service. Social level guides the forwarding of content requests to a content lookup service node. Social tie is exploited to deliver content requests to the content provider, and content data to the requester node. We leverage bounded random walks to estimate a node's centrality. The X-means clustering algorithm is used to compute a node's social level. Lastly, a node's social tie is computed based on the frequency and recency of node contacts. Extensive real-trace-driven simulation results show that our scheme requires less control overhead while maintaining comparable performance for content retrieval applications.

Abstract In this paper, we discuss scalable content‐oriented routing that enables storing, sharing, and searching data totally within the urban VANET. We introduce a scalable proactive content discovery scheme, hierarchical bloom‐filter routing (HBFR), to tackle mobility, large population, and rich content challenges of VANETs. Our simulation results show that HBFR achieves low latency and high content availability with relatively low overhead in practical VANET scenarios. In particular, HBFR improves the response time by up to 45% compared with the conventional Content Centric Networking (CCN) and reduces the traffic by up to 85% compared with timer‐based intelligent content search. HBFR suits the popular private data services the best and also achieves low response time comparable with that of flooding‐based content discovery when applying to popular public data services.Copyright © 2014 John Wiley & Sons, Ltd.

To access the Internet, companies define a Service Level Agreement (SLA) with Internet Service Providers (ISPs). Nevertheless, the current Internet does not assure Quality of Service (QoS), what points toward the concept of network virtualization and software defined network (SDN) to support the Future Internet. Moreover, the initial parameters defined in SLAs may not withstand traffic changes, resulting in a lower quality experienced by users and a waste of resources for ISPs. Within this context, this paper proposes an architecture to deal with resource usage variations. The proposal aims to enhance the QoS provided by the ISPs, while improving the usage of network resources in dynamic scenarios. Experiments using real traffic demonstrate the effectiveness of the proposed architecture.

Intra-flow network coding was proposed in recent years as a way of enhancing TCP performance over wireless networks. Transmission reliability is improved by sending redundant coded packets instead of retransmitting data packets. In this paper, we discuss the complex issue of TCP interaction with network coding and identify how network coding hides indistinctively link and congestion losses from TCP. Thus, some congestion losses do not trigger TCP congestion window reduction mechanisms. We then focus on fairness issues between coded and non-coded flows. As coded flows are less sensitive than non-coded flows to congestion losses, it prevents them from being as good as non-coded ones at reacting to congestion, making them greedier. We compare the performance of competing Pipeline-coded and non-coded flows in a bottleneck topology. In order to evaluate the fairness of coded flows, we introduce a new fairness index, given that coded flows normally perform better on lossy links without necessarily impacting non-coded flows. Our results show that unfairness exists, but it does interestingly not impact highly, because even with relatively high redundancy factors, non-coded flows do not starve. It shows that congestion losses are correlated enough to enable TCP over coding to react to the signal.

We address the problem of shock wave formation in uncoordinated highway traffic. First, we identify the combination of heavy traffic and small traffic perturbations or unexpected driver actions as the main causes of highway traffic jams. Then we introduce a novel distributed communication protocol that enables us to eliminate upstream shock wave formation even with low system penetration rates. Based on traffic information ahead, we propose a Cooperative Advanced Driver Assistance System (CADAS) that recommends non-intuitive velocity reductions in order to redistribute traffic more uniformly thereby eliminating traffic peaks. Simulation results show that CADAS significantly increases the average velocity and therewith reduces the overall travel time and avoids unnecessary slowdowns.

New vehicle applications have recently emerged, ranging from navigation safety to location aware content distribution and intelligent transport. These applications require efficient communications support. For example in a world of autonomous vehicles, V2V communications will be essential for stable cruise control and platooning. Vehicles will provide services to fellow drivers (e.g., congestion or spectrum crowd sourcing) as well as to external customers. An example of the latter is urban sensing. Vehicles have become rich sensor platforms. They can monitor the environment and classify events, e.g., license plates, chemical readings, etc. They generate metadata that can be used to resolve Insurance claims after minor road accidents or even assist Law Enforcement Agents in the forensic investigation of crimes. The Service notion suggests that the VANET can be viewed as a Mobile Computing Cloud (MCC) where vehicles interact and collaborate to provide Mobile Services not available from the Internet Cloud. This vision is corroborated by two emerging realities: the vehicles pick up too much multimedia information from the environment to possibly upload it all to the Internet Cloud. Moreover, time sensitive safety applications require the data to be processed locally in the vehicles. In this talk we revisit VANET applications and services and propose a Mobile Cloud vehicle services platform. We then discuss a specific example based on content creation, search and dissemination. We conclude by making the case for a uniform services platform that can support a broad range of vendors and applications.

Software-Defined Networking (SDN) is an emerging technology which brings flexibility and programmability to networks and introduces new services and features. However, most SDN architectures have been designed for wired infrastructures, especially in the data center space, and primary trends for wireless and mobile SDN are on the access network and the wireless backhaul. In this paper, we propose several designs for SDN-based Mobile Cloud architectures, focusing on Ad hoc networks. We present the required core components to build SDN-based Mobile Cloud, including variations that are required to accommodate different wireless environments, such as mobility and unreliable wireless link conditions. We also introduce several instances of the proposed architectures based on frequency selection of wireless transmission that are designed around different use cases of SDN-based Mobile Cloud. We demonstrate the feasibility of our architecture by implementing SDN-based routing in the mobile cloud and comparing it with traditional Mobile Ad Hoc Network (MANET) routing. The feasibility of our architecture is shown by achieving high packet delivery ratio with acceptable overhead.

In vehicular safety systems, two types of safety messages are required: Emergency Safety Message (ESM) and Periodic Beacon Message (PBM). The ESM has to be disseminated within a specified area with stringent delay and delivery ratio requirements, while the PBM does not need to meet these requirements. For exchanging the safety messages in Vehicular Ad-hoc NETwork (VANET), Inter-Vehicle Communication (IVC) is necessary whose de facto standard is Dedicated Short-Range Communications (DSRC). However, the effective transmission range in the DSRC-based IVC is short since a signal can be attenuated due to blocking by obstacles. In order to cover a large dissemination area in the DSRC-based IVC, multi-hop dissemination is required, which however causes channel collision and network congestion. Moreover, the coexistence with PBMs aggravates the collision and the congestion, which make it hard to satisfy the requirements of the ESM dissemination. To overcome the limitation of the DSRC, we utilize an extra TV White Space (TVWS) band that has a large communication range for ESM disseminations, and exploit a DSRC band for 1) the exchange of control data and 2) the compensation of ESM reception errors. In this paper, we propose and analyze a distributed channel usage framework that exploits advantages of DSRC and TVWS bands for ESM dissemination under the existence of PBMs. Our scheme employs TVWS Channel Rendezvous Algorithm (TCRA), ensuring that vehicles within a dissemination area select the same channel with the ESM sender. To compensate ESM reception failures in a TVWS band, our scheme adopts Two-Way Recovery Algorithm (TWRA) that uses DSRC and TVWS bands for ESM retransmission. Further, we establish an analytical delivery ratio model that considers a delay bound of an ESM for optimal parameter selections. To the best of our knowledge, this is the first attempt to propose a distributed channel usage scheme that leverages the strengths of TVWS and DSRC bands for safety message dissemination. Through an in-depth simulation study, we show that the proposed scheme satisfies ESM requirements for latency and packet delivery ratio, and outperforms previous approaches in various vehicular scenarios.

Mobile underwater networks with acoustic communications are confronted with several unique challenges such as long propagation delays, high transmission power consumption, and node mobility. In particular, slow signal propagation permits multiple packets to concurrently travel in the underwater channel, which must be exploited to improve the overall throughput. To this end, we propose the delay-aware opportunistic transmission scheduling (DOTS) protocol that uses passively obtained local information (i.e., neighboring nodes' propagation delay map and their expected transmission schedules) to increase the chances of concurrent transmissions while reducing the likelihood of collisions. Our extensive simulation results document that DOTS outperforms existing solutions and provides fair medium access even with node mobility.

Despite the popularity of mobile pay-for-answer Q&A services, little is known about the people who answer questions on these services. In this paper we examine 18.8 million question and answer pairs from Jisiklog, the largest mobile pay-foranswer Q&A service in Korea, and the results of a complementary survey study of 245 Jisiklog workers. The data are used to investigate key motivators of participation, working strategies of experienced users, and longitudinal interaction dynamics. We find that answerers are rarely motivated by social factors but are motivated by financial incentives and intrinsic motives. Additionally, although answers are provided quickly, an answerer's topic selection tends to be broad, with experienced workers employing unique strategies to answer questions and judge relevance. Finally, analysis of longitudinal working patterns and community dynamics demonstrate the robustness of mobile pay-for-answer Q&A. These findings have significant implications on the design of mobile pay-for-answer Q&A.

Recently, academic researchers and car manufactures have directed major efforts to develop active safety systems for reducing car accidents. In particular, for work zones they proposed to use smart cones that send a warning radio message to vehicles when the smart cones detect the possibility of an accident. The dominant protocol for vehicular communication is Dedicated Short Range Communications (DSRC), where Enhanced Distributed Channel Access (EDCA) and Hybrid Coordination Function (HCF) Controlled Channel Access (HCCA) are the MAC protocol options. Even though two MAC protocols are specified in the standard, there has been no attempt to use two protocols cooperatively nor to study the performance of such hybrid system in an actual vehicular network. In this paper, we examine for the first time the performance of a system that exploits EDCA and HCCA concurrently in vehicular networks. In particular, we concentrate on interaction between two MAC protocols and how much the interaction affects system performance. In addition, we investigate whether the system is feasible for work zone safety applications, and suggest guidelines for improvements based on our simulation findings.

Recently, Information Centric Networking (ICN) has attracted much attention also for mobiles. Unlike host-based communication models, ICN promotes data names as the first-class citizen in the network. However, the current ICN name-based routing requires Interests be routed by name to the nearest replica, implying the Interests are flooded in VANET. This introduces large overhead and consequently degrades wireless network performance. In order to maintain the efficiency of ICN implementation in VANET, we propose an opportunistic geo-inspired content based routing method. Our method utilizes the last encounter information of each node to infer the locations of content holders. With this information, the Interests can be geo-routed instead of being flooded to reduce the congestion level of the entire network. The simulation results show that our proposed method reduces the scope of flooding to less than two hops and improves retrieval rate by 1.42 times over flooding-based methods.

Mobile underwater networking is a developing technology for monitoring and exploring the Earth's oceans. For effective underwater exploration, multimedia communications such as sonar images and low resolution videos are becoming increasingly important. Unlike terrestrial RF communication, underwater networks rely on acoustic waves as a means of communication. Unfortunately, acoustic waves incur long propagation delays that typically lead to low throughput especially in protocols that require receiver feedback such as multimedia stream delivery. On the positive side, the long propagation delay permits multiple packets to be “pipelined” concurrently in the underwater channel, improving the overall throughput and enabling applications that require sustained bandwidth. To enable session multiplexing and pipelining, we propose the Multi-session FAMA (M-FAMA) algorithm. M-FAMA leverages passively-acquired local information (i.e., neighboring nodes' propagation delay maps and expected transmission schedules) to launch multiple simultaneous sessions. M-FAMA's greedy behavior is controlled by a Bandwidth Balancing algorithm that guarantees max-min fairness across multiple contending sources. Extensive simulation results show that M-FAMA significantly outperforms existing MAC protocols in representative streaming applications.

Many indoor localization techniques that rely on RF signals from wireless Access Points have been proposed in the last decade. In recent years, research on crowdsourced (also known as “Organic”) Wi-Fi fingerprint positioning systems has been attracting much attention. This participatory approach introduces new challenges that no previously proposed techniques have taken into account. This paper proposes “FreeLoc”, an efficient localization method addressing three major technical issues posed in crowdsourcing based systems. Our novel solution facilitates 1) extracting accurate fingerprint values from short RSS measurement times 2) calibration-free positioning across different devices and 3) maintaining a single fingerprint for each location in a radio map, irrespective of any number of uploaded data sets for a given location. Through experiments using four different smartphones, we evaluate our new indoor positioning method. The experimental results confirm that the proposed scheme provides consistent localization accuracy in an environment where the device heterogeneity and the multiple surveyor problems exist.

This paper presents the first prototype of Multipath Ad-hoc Data Network (MADN) a clean slate protocol for ad-hoc wireless content distribution. Inspired by the recent advances on Information Centric Networking (ICN), MADN is namely a pull-based protocol that emphasizes on seamless route redundancy and multi-path data delivery. It is complementary to the former IP protocol and therefore does not implement primitives for machine-to-machine communication. In consideration of targeting specifically the wireless medium, it uses rateless encoded data packets to counterbalance packet loss and to benefit from multi-source data distribution. A major difference between MADN and previous works is the use of the BlooGo algorithm in place of the conventional routing protocols - e.g. random walks, landmarks or coordinate spaces. The main advantages of using BlooGo is that it delivers the packets in considerably less hops while it maintains alternative routes open as backup of the shortest ones. This paper serves two aims, firstly it proposes a new protocol for multipath content distribution in ad-hoc environments, secondly it presents its architecture and how this interfaces with the final applications. Ultimately, the implementation is intentionally kept modular in order to facilitate deploying and evaluation of new solutions and new configurations - e.g. different caching algorithms or different types of Erasure Codes - without major refactoring of the codebase.

Geographic routing in Vehicular Sensor Networks (VSNs) has been considered as an efficient and scalable approach since it exploits location information instead of topology information to route data packets. Geographic routing requires sources to be aware of the location information of destinations. Many solutions have been proposed to provide the location information of destinations in ad hoc and sensor networks. However, they are not suitable and energy-efficient for VSNs because the field property of VSNs is very different from that of ad hoc and sensor networks. In VSNs, sensor nodes are deployed on roads and vehicles also moves on the roads. Thus, we propose a quorum-based location service scheme to provide source nodes with the location information of the vehicles in VSNs. The proposed scheme exploits the property of the road map in VSNs. For providing location service, a location query makes a quadrangular path quorum and a location update makes a line path quorum. Then, the proposed scheme guarantees a crossing point between the quadrangular path quorum and the line path quorum. A sensor node on the crossing point sends a location reply to source nodes. The source nodes deliver their data to the vehicle via geographic routing. For data delivery to the moving vehicles, we also propose a mobility supporting scheme. Simulation results shows that the proposed scheme has better performance than the existing scheme in terms of the number of transmitted and received packets and the location service delay.

In this paper, we discuss scalable content-oriented routing that enables storing, sharing and searching data totally within the VANET. We introduce a proactive content discovery scheme, Hierarchical Bloom-Filter Routing (HBFR), to tackle mobility, large population and rich content challenges of VANETs. HBFR is compared to the popular ICN reactive content discovery scheme in practical VANET scenarios. The results show that HBFR suits non-sharable data services, while reactive ICN inspired content discovery works well with popular sharable data. We suggest a hybrid approach that adaptively utilizes proactive and reactive schemes for time-sensitive data in ICN VANET.

First responders at the edge of the network rely on situation awareness updates to arrive in a timely matter, even when the fixed infrastructure is unavailable. The technical advancements of the commercial mobile phones make them capable of supporting such requirements under very disruptive network conditions. In this demo, we present a network architecture that exploits partial caches by utilizing network coding to deliver large files (e.g. images) to first responders. The architecture is based on a content centric network platform called ICEMAN(Information CEntric Mobile Ad-hoc Networking) and runs on Android phones. We demonstrate our system in a file dissemination scenario in a CORE/EMANE network emulation. We measure file delivery ratio, latency, and network overhead and report significant improvements that network coding achieves over fragmentation.

Indoor localization has attracted much attention recently due to its potential for realizing indoor location-aware application services. This paper considers a time-critical scenario with a team of soldiers or first responders conducting emergency mission operations in a large building in which infrastructure-based localization is not feasible (e.g., due to management/installation costs, power outage, terrorist attacks). To this end, we design and implement a collaborative indoor positioning scheme (CLIPS) that requires no preexisting indoor infrastructure. We assume that each user has a received signal strength map for the area in reference. This is used by the application to compare and select a set of feasible positions, when the device receives actual signal strength values at run time. Then, dead reckoning is performed to remove invalid candidate coordinates eventually leaving only the correct one which can be shared amongst the team. Our evaluation results from an Android-based testbed show that CLIPS converges to an accurate set of coordinates much faster than existing noncollaborative schemes (more than 50% improvement under the considered scenarios).

As the availability of LTE grows, the support of LTE to vehicular safety applications has been studied in recent years. One problem that was studied is the capability of beacon delivery. Due to the limited bandwidth, it is possible that not all vehicles can be served at the same time. A prioritization scheme should be used to satisfy the needs of applications. In this paper, we proposed a priority-based congestion control algorithm for cross-traffic assistance on LTE networks. All UEs are prioritized based on criteria such as distance to an intersection or arrival time to an intersection. If the load of the cell reaches the limit, low priority users will be disconnected in order to serve high priority users. Simulations show that the priority scheme can serve the needs of cross-traffic assistance service.

Welcome to HotMesh 2013: The Fifth IEEE International Workshop on Hot Topics in Mesh Networking. After the very successful editions in Europe (Lucca, Italy) two years ago and in the U.S. last year, we are happy to host this year the workshop in Europe again.

The Energy Service Interface (ESI), sitting at the boundary of a customer facility, plays a communication gateway role - interconnecting internal customer energy resources to external systems. A number of customer energy services are realized over the interconnected communications, which then contributes to smart grid interoperation eventually. In this paper, we examine the design issues of the ESI. To facilitate bi-directional customer energy services, the ESI must serve as both a service consumer and a service provider. At the same time, it must protect the customer energy resources from external threats and maximize the interoperation. To verify the issues, we build and deploy two ESI testbeds. Throughout experiments with a couple of energy service scenarios, we verify that the ESI plays the service "prosumer" in an interoperable manner. We also evaluate the performance of the security mechanism applied to the ESI and examine the potential of exploiting the Cloud technology for the ESI deployment. To the best of authors' knowledge, this is the first deployment of the ESI that addresses the fundamental, functional requirements.

Vehicular ad hoc networks (VANETs) provide the communication framework for the dissemination of safety-critical messages such as beacons and emergency messages. The communication channel witnesses significant network load generated by frequently exchanged beacons. Under high-density situations, it leads to a serious scalability problem in VANETs. Moreover, contention-based medium access control (MAC) protocols suffer from a great number of packet collisions, and as a result, the reliability and latency of safety messages are severely affected. Because of the periodic nature of beacons, time-division multiple access (TDMA) can be a good choice over contention-based MAC. In this paper, we propose congestion-controlled-coordinator-based MAC (CCC-MAC), which is a time-slot-based medium access protocol that addresses beacons and emergency messages. Basically, the network is virtually partitioned into a number of segments. Within a segment, medium access is accomplished by using a time-slot-scheduling mechanism supervised by a local coordinator vehicle. A significant number of vehicles can be supported under the proposed configuration. In fact, the proposed scheduling mitigates channel congestion by reducing the transmission time of beacons through the use of multiple data rates. Bandwidth utilization is also improved by reusing the unoccupied time slots. Finally, CCC-MAC ensures fast and reliable propagation of emergency messages by employing a pulse-based reservation mechanism. In the simulations, we demonstrate the ability of CCC-MAC to scale well in different vehicular density scenarios. Moreover, it outperforms existing MAC-layer protocols with respect to packet reception probability and latency of safety messages.

Using advanced wireless local area network technologies, vehicular ad hoc networks (VANETs) have become viable and valuable for their wide variety of novel applications, such as road safety, multimedia content sharing, commerce on wheels, etc. Multihop information dissemination in VANETs is constrained by the high mobility of vehicles and the frequent disconnections. Currently, geographic routing protocols are widely adopted for VANETs as they do not require route construction and route maintenance phases. Again, with connectivity awareness, they perform well in terms of reliable delivery. To obtain destination position, some protocols use flooding, which can be detrimental in city environments. Further, in the case of sparse and void regions, frequent use of the recovery strategy elevates hop count. Some geographic routing protocols adopt the minimum weighted algorithm based on distance or connectivity to select intermediate intersections. However, the shortest path or the path with higher connectivity may include numerous intermediate intersections. As a result, these protocols yield routing paths with higher hop count. In this paper, we propose a hop greedy routing scheme that yields a routing path with the minimum number of intermediate intersection nodes while taking connectivity into consideration. Moreover, we introduce back-bone nodes that play a key role in providing connectivity status around an intersection. Apart from this, by tracking the movement of source as well as destination, the back-bone nodes enable a packet to be forwarded in the changed direction. Simulation results signify the benefits of the proposed routing strategy in terms of high packet delivery ratio and shorter end-to-end delay.

Underwater mobile sensor networks have recently been proposed as a way to explore and observe the ocean, providing 4D (space and time) monitoring of underwater environments. We consider a specialized geographic routing problem called pressure routing that directs a packet to any sonobuoy on the surface based on depth information available from on-board pressure gauges. The main challenge of pressure routing in sparse underwater networks has been the efficient handling of 3D voids. In this respect, it was recently proven that the greedy stateless perimeter routing method, very popular in 2D networks, cannot be extended to void recovery in 3D networks. Available heuristics for 3D void recovery require expensive flooding. In this paper, we propose a Void-Aware Pressure Routing (VAPR) protocol that uses sequence number, hop count and depth information embedded in periodic beacons to set up next-hop direction and to build a directional trail to the closest sonobuoy. Using this trail, opportunistic directional forwarding can be efficiently performed even in the presence of voids. The contribution of this paper is twofold: a robust soft-state routing protocol that supports opportunistic directional forwarding; and a new framework to attain loop freedom in static and mobile underwater networks to guarantee packet delivery. Extensive simulation results show that VAPR outperforms existing solutions.

Content distribution in vehicular networks, such as multimedia file sharing and software updates, poses a great challenge due to network dynamics and high-speed mobility. In recent years, network coding has been shown to efficiently support distribution of content in such dynamic environments, thereby considerably enhancing the performance. However, the related work in the literature has mostly focused on theoretic or algorithmic aspects of network coding so far. In this paper, we provide an in-depth analysis on the implementation issues of network coding in wireless networks. In particular, we study the impact of resource constraints (namely CPU, disk, memory, and bandwidth) on the performance of network coding in the content distribution application. The contribution of this paper is twofold. First, we develop an abstract model of a general network coding process and evaluate the validity of the model via several experiments on real systems. This model enables us to find the key resource constraints that influence the network coding strategy and thus to efficiently configure network coding parameters in wireless networks. Second, we propose schemes that considerably improve the performance of network coding under resource constrained environments. We implement our overhead model in the QualNet network simulator and evaluate these schemes in a large-scale vehicular network. Our results show that the proposed schemes can significantly improve the network coding performance by reducing the coding overhead.

ABSTRACT The mobile revolution has brought us the possibility to enjoy our favorite applications anywhere and anytime. In this context, interactive games over mobile networks embody a fascinating case study both for their commercial success and for their technical challenges, thus, sparking interest and development. The current state of the art of interactive games over mobile networks is captured in this article. We discuss main requirements and analyze possible combinations of existing solutions to provide better support for highly interactive game sessions with mobile players. Copyright © 2012 John Wiley & Sons, Ltd.

This paper focuses on routing for vehicles getting access to infrastructure either directly or via multiple hops though other vehicles. We study Routing Protocol for Low power and lossy networks (RPL), a tree-based routing protocol designed for sensor networks. Many design elements from RPL are transferable to the vehicular environment. We provide a simulation performance study of RPL and RPL tuning in VANETs. More specifically, we seek to study the impact of RPL's various parameters and external factors (e.g., various timers and speeds) on its performance and obtain insights on RPL tuning for its use in VANETs.

Sickle Cell Disease (SCD) is a common chronic inherited disorder of red blood cells requiring careful pain management, particularly for youth. Clinicians and researchers have developed efficient pain management methods, from the traditional paper and pencil method to the computer-based electronic diaries (e-Diary). With the recent proliferation of smartphones and the advancement in mobile Internet connectivity, a new healthcare technology has become available. This paper presents a mobile e-Diary platform for youth with SCD utilizing the Internet capability of modern mobile phones. Unlike previous e-Diary systems ours is completely based on the Web technology, thus it has the advantage of platform-independence. The proposed system is designed to help children write everyday diary and provide appropriate pain management by healthcare providers. The usability and reliability of the system was evaluated with youths with SCD in conjunction with the UCLA Nursing School during 6-month study period. Our pilot study confirmed that the proposed web-based mobile e-Diary system could be used as a template for other pediatric chronic illnesses interventions in youth with other chronic illnesses.

Overlay network architectures that use orthogonal channels have been known to provide effective additional resources to underlying networks in high demand. Overlays are composed of relay nodes provided with rich computational resources and multiple wireless interfaces that make them capable of establishing several non-interfering networks. These networks can be used to move traffic around in a non-interfering manner. It is possible to deploy such overlays in sensor networks where sensors suffer from the funnel effect caused by excess traffic flows, to help mitigate this effect. In this paper we address the geographical placement of relay nodes in the region to mitigate the funnel effect in sensor networks. We provide an O (mlog (h) ) algorithm of congested region size m and computed Convex Hull size h that finds the placement of the minimum number of relay nodes to cover the entire congested region. In a greedy fashion, we place a relay node given the following placement conditions: the closest position such that it covers the largest amount of peers up to an extent parameter bounded by its transmission range, and that is closest to the sink. Our simulated results show that using a minimum number of relays, we could save up to 43% of nodes compared to a simple placement strategy, the underlying network increases its delivery ratio and throughput, improves its jitter, and opens the possibility of load balancing and fairness advantages.

In this paper we address the problem of uncoordinated highway traffic. We first identify the main causes of the capacity drop, namely high traffic demand and inadequate driver reaction. In the past, traffic and user behavior have been accurately described by cellular automata (CA) models. In this paper we extend the CA model to deal with highway traffic fluctuations and jams. Specifically, the model incorporates the communication layer between vehicles. The model thus enables us to study the impact of inter-vehicular communications and in particular the delivery of critical and timely upstream traffic information on driver reaction. Based on the newly-available traffic metrics, we propose an Advanced Driver Assistance System (ADAS) that suggests non-intuitive speed reduction in order to avoid the formation of so-called phantom jams. The results show that using such a system considerably increases the overall traffic flow, reduces travel time and avoids unnecessary slow-downs.

TCP over Mobile Ad-hoc Networks (MANETs) is challenging due to frequent route breaks, high random errors, and DATA-ACK interference. Network coded multipath approaches have been shown in several previous studies to be an effective transmission paradigms in disruptive networks. However, most of the previous studies either have no adaptive redundancy control or rely on theoretical models that require knowledge at all relays of the entire network state. In this paper, we propose a network coded multipath scheme for conventional TCPCodeMP that adapts to frequent link changes in MANET and requires no explicit control messages. The scheme exploits multiple-path redundancy and maintains total transparency to transport layer protocols. The proposed coding scheme is based on three components: (1) random linear coding scheme with adjustable redundancy, (2) multipath routing, (3) ACK Piggy coding. Simulation results show that in a 3-hop static scenario, the proposed multipath scheme improves TCP flows goodput by 70% compared to our previous single-path scheme. In an extreme MANET scenario where two TCP sessions co-exists and nodes are moving as fast as 25 m/s with up to 40% packet error rate (an environment in which regular TCP collapses completely), CodeMP achieves at least 700Kbps aggregate TCP goodput, with a Jain's fairness index of 0.99.

Automated platooning is one of the most challenging fields in the domain of ITS. Conceptually, platooning means creating clusters of vehicles which closely follow each other autonomously without action of the driver, neither for accelerating, nor for braking.

Welcome to HotMesh 2012: The Fourth IEEE International Workshop on Hot Topics in Mesh Networking. After the very successful edition in Europe (Lucca, Italy) last year we are happy to host this year workshop in the U.S.

Dengue is a disease transmitted primarily through mosquito bites. Innovative solutions have been developed to combat outbreaks. However, in developing countries these dengue detection solutions are often not affordable and easily accessible. Additionally, these traditional approaches are slow to diagnose and treat dengue. We present a dengue detection solution that uses vision sensors in cellular phones, a lightweight object identification algorithm, and a web server that provides spatial information to healthcare providers. Our systems leverages a novel paper based technology developed by researchers at the Harvard University Department of Chemistry (Martinez et al. Angew Chem Int Ed 46:1318–1320, 2007 ). Our dengue detection algorithm rapidly diagnoses dengue, transmits the results to the Center for Disease Control (CDC) for further analysis, and presents healthcare providers with spatial information on outbreaks. This novel approach can improve the quality of life in developing countries by accurately and economically detecting dengue and providing data to the CDC for monitoring of dengue epidemics.

Vehicular ad hoc networks (VANETs) enable vehicles to communicate with each other but require efficient and robust routing protocols for their success. In this paper, we exploit the infrastructure of roadside units (RSUs) to efficiently and reliably route packets in VANETs. Our system operates by using vehicles to carry and forward messages from a source vehicle to a nearby RSU and, if needed, route these messages through the RSU network and, finally send them from an RSU to the destination vehicle. Our system is mostly critical for users who are far apart and want to communicate using their vehicles' onboard units. Many recent paradigms, like social networks, will greatly benefit from a system like ours to enable users on the road to exchange different types of data. We evaluate the performance of our system using the ns2 simulation platform and compare our scheme to existing solutions. The results prove the feasibility and efficiency of our scheme.

Large military ad hoc networks are often characterized by the interconnection of heterogeneous domains. The same trend is emerging in civilian MANETs (e.g., search and rescue, vehicular networks). In these networks it is important to be able to efficiently propagate information across domains in multicast mode (e.g., situation awareness dissemination, commands, streams). Several multicast protocols have been developed for single domain MANET. However, few can be extended to inter-domain operation. In fact, multicast routing across different MANET domains faces the challenges of node motion, topology changes, dynamic gateway election and, possibly, connectivity interruption. To overcome these challenges, especially to achieve routing scalability and at the same time maintains efficient routing, this paper proposes the Geo-assisted Multicast Inter-domain Routing (GMIDR) protocol based on geographical assistance and cluster technology. Intensive simulation results show that the GMIDR protocol is scalable and stable with various numbers of multicast group members, and it outperforms other multicast protocols. A military use case scenario simulation shows that GMIDR can be utilized efficiently in the large scale networks crossing multiple domains. Geocast by applying GMIDR shows the flexibility of the protocol.

Vehicular communications promise to bring us safer driving and better traffic control. Dedicated Short Range Communications (DSRC) and IEEE 802.11p are now well established standards for the inter-vehicle and vehicle-to-road side unit (RSU) communication. These channels, however, are of limited capacity and are not sufficient to support the broad range of services envisioned in VANETs. Thus, vehicles will utilize WiFi (802.11 a/b/g) and unlicensed ISM band to acquire more capacity. Unfortunately, the WiFi channels in urban area are already heavily subscribed by residential customers. In this paper, we propose CoVanet, a cognitive vehicular ad hoc network architecture that allows vehicles opportunistic access to WiFi channels. CoVanet is the first approach to use cognitive radios in a VANET. It differs from conventional cognitive radio strategies in that it uses unlicensed band and operates in an ad hoc, multihop mode. In CoVanet, network topology and channel environment change frequently due to high node mobility. The main contribution of this work is a Cognitive Ad hoc Vehicular Routing Protocol (CoRoute) that utilizes geographical location and sensed channel information. Simulation results demonstrate CoRoute efficiency and robustness to mobility and external interference.

On behalf of the Technical Program Committee, we welcome all of you to the IEEE International Wireless Communications and Mobile Computing Conference (IEEE IWCMC 2011) in the beautiful campus of Bahcesehir University, Istanbul, Turkey! We are indeed delighted that this year's IEEE IWCMC accomplishes its goal under the conference theme “Making Wireless Communities,” and continues its tradition of providing the premier forum for presentation of research results and experience reporting on the cutting edge research in the general areas of wireless communications and mobile computing. This year, we received more than 1000 submissions from 51 countries worldwide. Each paper received at least three peer technical reviews, comprised of 49 Symposia Chairs/Co-Chairs and a total of more than 450 TPC members from academia, government laboratories, and industries. After carefully examining all the received review reports, the IEEE IWCMC 2011 TPC finally selected about 35% high-quality papers for presentation at the conference and publication in the IEEE IWCMC 2011 proceedings. The conference program starts on Monday July 4thwith a full day Tutorials that is free of charge to all our attendees. Then, each day starts with a keynote speaker chosen from renowned world-class leaders in the area-Dr. Rick Stevens, Dr. Mario Gerla, and Dr. Sajal Das, highlighting the latest research trends in the wireless communications, mobile computing, and networks. This year, the technical sessions reflect the continued and growing interests in a wide range of spectrum, including wireless communications and networks, cross-layer design and optimization, mobile computing, wireless sensor networks, network security, and use of wireless technologies in social emergency applications. We also added a special Workshop this year to address practical aspects of Wireless Communications and Mobile Computing, such as Multihop Wireless Network Testbeds and Experiments, Network and Communications for Advanced Society, and Federated Wireless Sensor Systems (FedSenS). There are five special sessions composed of invited papers from renowned experts from around the world. Outstanding papers will be selected for four Special Issues in well known international journals. Our objective in the future is to reduce the acceptance rate further to reach 30% and less. In addition, we would like to reduce the number of Symposia and Workshops as well to meet the conference theme.

The emergence of multi-channel wireless networks and cognitive radio networks has rendered dynamic channel selection an important task, and many existing channel selection schemes factor in the amount of wireless activities that take place in each channel, or channel load, to achieve load balance and maximize the utilization of wireless resources. In such environments, a monitoring node must sense the channel to estimate the channel load, yet when the node is equipped with a single radio interface, in which case the lone interface must be used for both channel sensing and data communication, there can be only a fixed amount of time allotted to channel sensing. In this paper, we show that a careful scheduling of channel sensing is needed to improve the accuracy of channel load estimation, and based on our findings, we devise a sensing strategy that minimizes the estimation error. Evaluation shows that our scheme can reduce the relative estimation error by as much as 40% in a heavily loaded channel environment.

Cognitive radio network research has mostly focused on licensed spectrum sensing and empty spectrum use while protecting licensed band primary users. However, the wide deployment of WiFi access points in unlicensed bands in urban areas brings difficult challenges regarding co-existence of ad hoc mobile users with residential access points. In this paper, we propose a new mobile user protocol for dynamic channel selection via channel workload estimation. The mobile node senses channel usage in unlicensed ISM band and selects the maximum residual capacity channel for own packet transmission. The new protocol is implemented on Microsoft's SORA software defined radio system that enables fast prototyping. We have evaluated the performance using a Campus deployed SORA testbed. Experimental results show the efficiency of our approach in avoiding external interference.

In this paper, we consider the use of unlicensed Wi-Fi band for vehicular ad hoc networks. In particular, we focus on exploiting channelization to improve spatial reuse, and avoiding interference that is external to the vehicular network. To this end, we propose Cognitive Channel Hopping (CCH), a decentralized channel hopping protocol where nodes select their channels based on cognitively collected channel quality measurements, in a manner that the network's connectivity is maintained. Our evaluation shows that CCH can take advantage of multiple channels that are available to significantly improve the network performance over a single-channel network, and can effectively tolerate external interference.

Traditional directional broadcast protocols for VANETs always select redundant nodes and thus are not very efficient. Road-based directional broadcast was proposed to solve this problem. The basic idea is to categorize vehicles based on road topology and select a relay for each road. It improves the efficiency significantly, but data propagation could fail due to collisions. In this paper, we aim to add reliability to road-based directional broadcast protocol. A MAC layer collision avoidance scheme is proposed to reduce the chance of collision between the sender and the selected relay nodes, while other nodes can receive data opportunistically. By limiting the number of selected relays, this scheme improves the delivery ratio than that of traditional broadcast protocols while keeping the efficiency at a comparable level.

It is our great pleasure to welcome you to the twelfth edition of the IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM 2011), taking place in the historical and charming city of Lucca, at the very heart of Tuscany, Italy, on June 20–23, 2011.

Urban-X is a new architecture for Multi-Radio Cognitive Mesh Networks based on principles from Dynamic Spectrum Access Networks. In the Urban-X, spectrum sensing and mobility are challenging a transport control protocol (TCP) whose performance is sensitive to varying delay and available bandwidth. Also high packet loss due to primary users lets standard TCP to operate inefficiently. In this study, we propose a new transport protocol TP-UrbanX for the Urban-X which exploits reinforcement based learning techniques to learn an optimal sending rate and adapt this rate given the dynamics of the environment such as spectrum sensing and channel mobility.

Advances in portable technologies and emergence of new applications stimulate interest in urban vehicular communications for commercial, military, and homeland defense applications. Simulation is an essential tool to study the behavior and evaluate the performance of protocols and applications in large-scale urban vehicular ad hoc networks (VANET). In this paper, we propose CORNER, a low computational cost yet accurate urban propagation model for mobile networks. CORNER estimates the presence of buildings and obstacles along the signal path using information extrapolated from urban digital maps. A reverse geocoding algorithm is used to classify the propagation situation of any two nodes that need to communicate starting from their geographical coordinates. We classify the relative position of the sender and the receiver as in line of sight (LOS) or nonline of sight (NLOS). Based on this classification, we apply different formulas to compute the path loss (PL) metric. CORNER has been validated through extensive on-the-road experiments, the results show high accuracy in predicting the network connectivity. In addition, on-the-road experiments suggest the need to refine the fading model to differentiate between LOS, and NLOS situations. Finally, we show the impact of CORNER on simulation results for widely used applications.

Abstract An inelastic flow is a flow with an inelastic rate, i.e., the rate is fixed, and it cannot be dynamically adjusted to traffic and load condition as in elastic flows like TCP. Real time, interactive sessions, and video/audio streaming are typical examples of inelastic flows. Reliable support of inelastic flows in wirelessad hocnetworks is extremely challenging because flows and routes dynamically change and flows compete for the shared wireless channel. Bandwidth must be reserved for inelastic flows at session set up time. To avoid repeated attempts to set up reservations in a ‘volatile’ network and prevent serious network capacity degradation due to call set up overhead, a Call Admission Control strategy robust to mobility must be developed. In this paper we propose ProbeCast, a probe based call admission control scheme with QoS guarantees for inelastic flows. ProbCast was designed for multicast streams but can also work, by default, for unicast. In ProbeCast, a path (or a tree) is probed for capacity availability. If an intermediate link along the probed path fails to meet the QoS requirement, the flow is ‘pushed back’ via backpressure upstream to an intermediate branch or possibly to the source. The backpressure principle is simple; however, its implementation requires some care to avoid unfairness and eventual capture by one of the flows sharing a congested bottleneck. We show that proportional fairness among inelastic contenders will prevent capture. To achieve this, we have developed the Neighborhood Proportional Drop (N‐PROD) scheme. N‐PROD guarantees fair rejection of unfeasible flows and maintains the same proportional drop rate among surviving flows in the same contention domain. We demonstrate the efficacy and robustness of ProbeCast for unicast as well as multicast scenarios using the Qualnet simulation platform. Copyright © 2010 John Wiley & Sons, Ltd.

Road congestion results in a huge waste of time and productivity for millions of people. A possible way to deal with this problem is to have transportation authorities distribute traffic information to drivers, which, in turn, can decide (or be aided by a navigator) to route around congested areas. Such traffic information can be gathered by relying on static sensors placed at specific road locations (e.g., induction loops and video cameras) or by having single vehicles report their location, speed, and travel time. While the former approach has been widely exploited, the latter has come about only more recently; consequently, its potential is less understood. For this reason, in this paper, we study a realistic test case that allows the evaluation of the effectiveness of such a solution. As part of this process, (a) we designed a system that allows vehicles to crowd-source traffic information in an ad hoc manner, allowing them to dynamically reroute based on individually collected traffic information; (b) we implemented a realistic network-mobility simulator that allowed us to evaluate such a model; and (c) we performed a case study that evaluates whether such a decentralized system can help drivers to minimize trip times, which is the main focus of this paper. This study is based on traffic survey data from Portland, OR, and our results indicate that such navigation systems can indeed greatly improve traffic flow. Finally, to test the feasibility of our approach, we implemented our system and ran some real experiments at UCLA's C-Vet test bed.

Vehicular ad hoc networks (VANETs) have recently been considered as an attractive network architecture to provide various services ranging from road safety to entertainment applications. In this paper, we propose an IEEE-802.11-based multihop broadcast protocol to address the issue of emergency message dissemination in VANETs. The protocol adopts a binary-partition-based approach to repetitively divide the area inside the transmission range to obtain the furthest possible segment. The forwarding duty is then delegated to a vehicle chosen in that segment. Aside from accomplishing directional broadcast for highway scenario, the protocol also exhibits good adaptation to complex road structures. The main focus of the paper lies in reducing broadcast delay, which is an important factor for time-critical safety applications. Most importantly, the contention delay remains almost constant, irrespective of vehicle density. Mathematical analysis is performed to assess the effectiveness of the protocol. Simulation results demonstrate that the proposed protocol imparts greater performance in terms of latency and message progress when compared with contemporary multihop broadcast protocols for VANETs.

ABSTRACT Vehicular communications promise to bring us safer driving and better traffic control. Dedicated short range communications and IEEE 802.11p are now well established standards for vehicular communications. Channels for those systems, however, are of limited capacity and are dedicated to safety applications. Thus, they are not sufficient to support the broad range of services envisioned in VANETs. It is anticipated that vehicles will utilize Wi‐Fi (802.11 a/b/g) to acquire more capacity. Unfortunately, the Wi‐Fi channels in urban areas are already quite heavily subscribed by residential customers. To evade the residential load, in this paper, we propose CoVanet, a cognitive vehicular ad hoc network architecture that allows vehicle radios to access the Wi‐Fi channels ‘opportunistically’, finding least loaded channels. In CoVanet, network topology and channel environment change frequently because of high node mobility. The main contribution of this work is a cognitive ad hoc vehicular routing protocol (CoRoute). CoRoute is a hybrid that utilizes both geographical location and sensed channel information to establish stable, minimum delay routes to the destination. Simulation results show that CoRoute is robust to mobility and to external interference and improves packet delivery ratio on average by 70% with respect to routing without cognitive radios. Copyright © 2011 John Wiley & Sons, Ltd.

We propose a vehicular network trust model that integrates cryptography-based entity trust and email-based social trust. The entity trust provides security protections such as origin integrity, data integrity, and confidentiality. The social trust provides a level of belief on the data transmitted by an entity. To achieve the email-based social trust, we require each user to run an automated agent that performs trust evaluation checks and processes trust checking requests. The requests are from their highly trusted contacts or through a trusted proxy server maintained by the email service provider. We utilize identity-based cryptography (IBC) to integrate entity trust and social trust. This allows us to use a unique identity (e.g., an email address) for each entity. Further, we use the IBC based attribute based cryptography to develop secure group communications in vehicular networks. Finally, we present research challenges and potential research directions to extend this work.

In recent work it has been shown that the use of virtual coordinates or identifiers for efficient routing and data management has several advantages compared to the use of predefined addresses or geographical coordinates. However, these advantages only hold for single domain networks with limited mobility. In this paper, we discuss the challenges arising from using virtual coordinates for routing (to a particular sensor ID or to indexed data or resources) in ad hoc and sensor networks in multi-domain network scenarios. We show the feasibility of inter-domain routing by exploiting a concept that is central to most virtual coordinate approaches: the availability of data management operation using a DHT like mechanism. Based on the Virtual Cord Protocol (VCP), we show how inter-domain routing can be realized using appropriate indirections. Furthermore, we investigate the possibility of replicating data among different networks, or DHTs, to provide seamless data access in multi-domain environments. Our simulation results clearly show that both functions can be realized with only marginal overhead.

Underwater Acoustic Sensor Networks (UW-ASNs) use acoustic links as a means of communications and are accordingly confronted with long propagation delays, low bandwidth, and high transmission power consumption. This unique situation, however, permits multiple packets to concurrently propagate in the underwater channel, which must be exploited in order to improve the overall throughput. To this end, we propose the Delay-aware Opportunistic Transmission Scheduling (DOTS) algorithm that uses passively obtained local information (i.e., neighboring nodes' propagation delay map and their expected transmission schedules) to increase the chances of concurrent transmissions while reducing the likelihood of collisions. Our extensive simulation results document that DOTS outperforms existing solutions and provides fair medium access.

In the drive-thru Internet access systems, vehicles connect to road-side access points (APs) to use IP-based services, such as web-browsing, e-mail, and file download, in addition to the customized vehicular applications. However, the mobility of vehicles and the limited coverage of APs result in the short connectivity duration and low throughput, thus leading to low availability of Internet to vehicle services. Vehicle-to-vehicle (V2V) relay support is an attractive backup solution that can address these limitations by extending the coverage. To fully realize the benefit of V2V relay support, however, the vehicle that gives the best performance must be selected as relay, yet the dynamic wireless channel conditions and the high speed of vehicles render relay selection a challenging problem. In this paper, we evaluate several relay strategies in an analytic framework to compute the resulting overall network capacity with fading channels. We then propose and devise an efficient opportunistic relay protocol that exploits multiuser diversity and effectively copes with the dynamic channel. Through both capacity analysis and Qualnet simulations, we show that the opportunistic relay scheme significantly outperforms others.

A SEA Swarm (Sensor Equipped Aquatic Swarm) is a sensor "cloud" that drifts with water currents and enables 4D (space and time) monitoring of local underwater events such as contaminants, marine life and intruders. The swarm is escorted at the surface by drifting sonobuoys that collect the data from underwater sensors via acoustic modems and report it in real-time via radio to a monitoring center. The goal of this study is to design an efficient anycast routing algorithm for reliable underwater sensor event reporting to any one of the surface sonobuoys. Major challenges are the ocean current and the limited resources (bandwidth and energy). In this paper, we address these challenges and propose HydroCast, a hydraulic pressure based anycast routing protocol that exploits the measured pressure levels to route data to surface buoys. The paper makes the following contributions: a novel opportunistic routing mechanism to select the subset of forwarders that maximizes greedy progress yet limiting co-channel interference; and an efficient underwater "dead end" recovery method that outperforms recently proposed approaches. The proposed routing protocols are validated via extensive simulations.

A wireless mesh network (WMN) has been popularly researched as a wireless backbone for Internet access with off-the-shelf and inexpensive equipments. Nowadays, several applications like contents sharing, multicast video streaming, vehicular networks encourage to build mesh networks in urban areas. However, the deployment of WMNs in unlicensed bands of dense urban areas imposes many challenges. While previous research has mostly focused on optimal channel allocation under inter or intra-flow interferences within mesh nodes, the practical deployment of WMNs also requires to consider the interference caused by external entities such as residential access points that do not belong to the WMN. To address this issue, we propose Urban-X which is a first attempt towards a new architecture for Multi-Radio Cognitive Mesh Networks. Based on a cross-layer scheme, we develop novel routing and forwarding schemes reflecting the residential traffic state of external users. Through an extensive simulation analysis using the ns-2 simulator, we demonstrate the feasibility of our routing scheme and we show its robustness to the variations of channel environment and external traffics.

The advancements of diverse radio technologies and emerging applications have spawned increasing heterogeneity in mobile ad hoc networks (MANETs). But the collaborative nature of communications and operations often requires that these heterogeneous MANETs to be interoperable. Nonetheless, the existing interconnection protocols designed for the Internet (namely inter-domain routing protocol such as BGP) are not adequate for handling the unique challenges in MANETs. In this paper, we present a novel Inter-MANET Routing protocol called InterMR that can handle the heterogeneity and dynamics of MANETs. Our first contribution is an Inter-MANET address scheme based on a variety of node attributes (e.g., symbolic name, property, etc.); this allows dynamic merging/split of network topologies without a separate Name Server. Our second contribution is to provide a seamless routing mechanism across heterogeneous MANETs without modifying the internal routing mechanisms in each MANET. The proposed scheme can transparently adapt to topological changes due to node mobility in MANETs by dynamically assigning the gateway functionalities. We show, by packet-level simulation, that the performance of InterMR can be improved by up to 112% by adaptive gateway assignment functionalities. We also show that InterMR is scalable with only modest overhead by analysis.

AutoGait is a mobile platform that autonomously discovers a user's walking profile and accurately estimates the distance walked. The discovery is made by utilizing the GPS in the user's mobile device when the user is walking outdoors. This profile can then be used both indoors and outdoors to estimate the distance walked. To model the person's walking profile, we take advantage of the fact that a linear relationship exists between step frequency and stride length, which is unique to individuals and applies to everyone regardless of age. Autonomous calibration invisible to users allows the system to maintain a high level of accuracy under changing conditions. AutoGait can be integrated into any pedometer or indoor navigation software on handheld devices as long as they are equipped with GPS. The main contribution of this paper is two fold: (1) we propose an auto-calibration method that trains a person's walking profile by effectively processing noisy GPS readings, and (2) we build a prototype system and validate its performance by performing extensive experiments. Our experimental results confirm that the proposed auto-calibration method can accurately estimate a person's walking profile and thus significantly reduce the error rate.

Vehicular networks are on the fast track to become a reality either through a car manufacturer that introduces a communication device in the car electronics or through an aftermarket vendor such a GPS navigator or a in-vehicle entertainment system. This paper introduces VERGILIUS a nouvelle urban mobility and propagation toolbox designed to streamline the mobility trace generation and path loss computation in vehicular network studies. The aim of VERGILIUS is to enable a whole new level of simulation through the introduction of Urban Maps, finely tunable motion patterns, and detailed trace analysis.

There has been a variety of rate adaptation solutions proposed for both indoor and mobile scenarios. However, dynamic channel changing conditions (e.g., temporal channel variation due to unpredictable traffic pattern) make it virtually impossible to guarantee the same evaluation environment for all these schemes. Moreover, developing these schemes exhaustively on actual hardware can be gruesomely long. In this work, we propose an integrated framework which utilizes empirical data gathered from the vehicular testbed to objectively compare different rate adaptation schemes for Vehicular Ad-hoc Networks (VANETs). Using this framework, we implemented some well-known adaptation schemes and evaluated their performance. The main contribution of this paper is a methodology to compare rate adaptation schemes in an environment which is both realistic and repeatable. In addition, our results shed new light on impact of various different environment and channel factors on the performance of different schemes.

The Network Utility Maximization (NUM) has been extensively used in both wired and wireless networks and has been very helpful to provide insight on optimal controls of various parameters such as power, scheduling and rate control. However, the popular opportunistic scheduling mechanism, that improves the system performance by exploiting time varying channel conditions at different receivers, has not been incorporated in the framework yet. In this paper, we extend the framework and derive optimal flow control and link scheduling for wireless multihop networks with opportunistic scheduling. More precisely, we formulate the NUM problem with new resource constraints to include the benefits of opportunistic scheduling and then proceed to solve the problem. The formulation turns out to be a non-convex problem, however we propose an algorithm that approximates the optimum solution. Numerical results show that the proposed algorithm achieves significant throughput gain.

In the near future vehicular networks based on wireless technology will be part of our lives. Efficient and robust routing algorithms will play a key role in the success of such technology. In this paper we present TrafRoute, an efficient and robust routing scheme for vehicular networks, suitable for both Vehicle-to-Vehicle and Vehicle-to-Infrastructure communications. TrafRoute introduces a novel approach to routing that involves landmark-based routes and forwarder self-election, exploiting the knowledge of the underlying road network. We demonstrate TrafRoute's efficiency and robustness through simulation studies performed with accurate mobility and propagation models.

Abstract In this paper, we introduce a Mean Value Analysis (MVA)‐based methodology for the performance evaluation of transactions executed in a multi‐server distributed system. We first present probabilistic arguments to investigate under which conditions MVA models provide worst‐case response times, without large overshoots. Then, we show how to characterize the distributed server system so as to construct a model to predict response times as well as to estimate system capacity. Finally, we exemplify the methodology usage via transactions implemented in two distributed Linux systems. Copyright © 2010 John Wiley & Sons, Ltd.

The 11 papers in this special issue on mission critical networking are divided into three categories: quality of service issues (three papers); security issues (four papers); and configuration and data collection issues (four papers).

A SEA Swarm (Sensor Equipped Aquatic Swarm) is a collection of mobile underwater sensors that moves as a group with water current and enables 4D (space and time) monitoring of local underwater events such as contaminants and intruders. For prompt alert reporting, mobile sensors routes events to mobile sinks (i.e., autonomous underwater vehicles) via geographic routing that is known to be most efficient under mobility and scarce acoustic bandwidth. In order for a packet to be routed to the destination using geographical routing, it requires to know the location of the destination. This is accomplished by having a location service that returns the location of a requested node. Our goal is to design such location service for SEA Swarm. In this paper, we analyze various design choices to realize an efficient location service in SEA Swarm scenarios. We find that conventional ad hoc network location service protocols cannot be directly used, because the entire swarm moves along water current. We prove that maintaining location information in a 2D plane is a better design choice. Given this, we propose a bio-inspired location service called a Phero-Trail location service protocol. In Phero-Trail, location information is stored in a 2D upper hull of a SEA Swarm, and a mobile sink uses its trajectory (a la a pheromone trail of ants) projected to the 2D hull to maintain location information. This enables mobile sensors to efficiently locate a mobile sink. Our results show that Phero- Trail performs better than existing approaches.

Position-based routing has proven to be well suited for highly dynamic environment such as Vehicular Ad Hoc Networks (VANET) due to its simplicity. Greedy Perimeter Stateless Routing (GPSR) and Greedy Perimeter Coordinator Routing (GPCR) both use greedy algorithms to forward packets by selecting relays with the best progress towards the destination or use a recovery mode in case such solutions fail. These protocols could forward packets efficiently given that the underlying network is fully connected. However, the dynamic nature of vehicular network, such as vehicle density, traffic pattern, and radio obstacles could create unconnected networks partitions. To this end, we propose GeoDTN+Nav, a hybrid geographic routing solution enhancing the standard greedy and recovery modes exploiting the vehicular mobility and on-board vehicular navigation systems to efficiently deliver packets even in partitioned networks. GeoDTN+Nav outperforms standard geographic routing protocols such as GPSR and GPCR because it is able to estimate network partitions and then improves partitions reachability by using a store-carry-forward procedure when necessary. We propose a virtual navigation interface (VNI) to provide generalized route information to optimize such forwarding procedure. We finally evaluate the benefit of our approach first analytically and then with simulations. By using delay tolerant forwarding in sparse networks, GeoDTN+Nav greatly increases the packet delivery ratio of geographic routing protocols and provides comparable routing delay to benchmark DTN algorithms.

Vehicular Ad Hoc Network has recently been considered as attractive network architecture to provide various services ranging from road safety to entertainment applications. In this paper, we propose an IEEE 802.11 based multihop broadcast protocol to address the issue of safety message dissemination in Vehicular Ad Hoc Networks. This position- based protocol adopts a repetitive 2-partition method to divide the area inside transmission range resulting in a furthest narrow segment and delegates the forwarding duty to a vehicle chosen in the furthest segment. The main focus of the paper lies in reducing broadcast delay which is an important factor in time critical safety applications. We attempt to attain consistent performance irrespective of node density and different VANET scenarios. In addition to this, the protocol also solves the hidden terminal problem of multihop broadcasting. Simulation results show that our protocol achieves greater performance in terms of latency and message progress when compared with other well known multihop broadcast protocols for Vehicular Ad Hoc Networks.

In this paper, we introduce a mean value analysis based methodology for performance evaluation of transactions executed in a multi server distributed system. We first present probabilistic arguments to investigate under which conditions MVA models provide worst case response times, without large overshoots. Then, we show how to characterize the distributed server system so as to construct a model to predict response times as well as estimate system capacity. Finally, we exemplify the methodology usage via transactions implemented in two distributed Linux systems.

Simulation is essential to evaluate the performance of large scale vehicular networks. It is logistically challenging (and prohibitively expensive) to run tests with more than a few dozens experimental vehicles. Given the critical role of simulation in the evaluation of VANET protocols in large scale scenarios, it is important to guarantee realism of the models. This paper focuses on the accuracy of urban propagation models and their impact on vehicular protocol results. In a city-based vehicular network we compare the predominant two ray model and a recently proposed Corner model. We identify a number of factors that undermine the validity of the Two Ray model, for example, the presence of buildings causing propagation disruption and the heavy weight border effects that incorrectly compensate for the presence of hidden terminals in the networks. The paper analyzes a small scale urban vehicular scenario which unveils the issues to be considered in large scale vehicular simulations.

Providing vehicles' position is essential in VANETs. Currently, GPS positioning is widely used, but the accuracy is not adequate for emerging safety applications. In order to provide accurate positioning, this paper proposes RF-GPS, a RFID-assisted localization system that reliably supports lane-level position accuracy. It improves accuracy of the GPS system by employing a DGPS-like concept. It also allows vehicles without GPS to compute their position by contacting GPS equipped neighbors. We evaluate the performance of the proposed localization system via simulation.

Biochemical activities in sewer pipes generate various volatile substances that lead to several serious problems such as malodor complaints and lawsuits, concrete and metal corrosion, increased operational costs, and health risks. Frequent inspections are critical to maintain sewer health, yet are extremely expensive given the extent of the sewer system and the "unfriendliness" of the environment. In this paper we propose SewerSnort, a low cost, unmanned, fully automated in-sewer gas monitoring system. A sensor float is introduced at the upstream station and drifts to the end pumping station, collecting location tagged gas measurements. The retrieved SewerSnort provides an accurate gas exposure profile to be used for preventive maintenance and/or repair. The key innovations of SewerSnort are the fully automated, end-to-end monitoring solution and the low energy self localizing strategy. From the implementation standpoint, the key enablers are the float mechanical design that fits the sewer constraints and the embedded sensor design that matches the float form factor and complies with the tight energy constraints. Experiments based on a dry land emulator demonstrate the feasibility of the SewerSnort concept, in particular, the localization technique and the embedded sensor design.

Overcoming problems associated with network dynamicity and unreliable channels has been a challenge for data dissemination protocols in vehicular networks. In this paper, we present an overview on the most interesting solutions that have been proposed to perform data dissemination in this environment. Starting from this analysis, we present a novel approach that can efficiently address a reliable communication even in high dynamic networks. The new approach is based on the exploitation of a peculiar characteristic of rateless codes. In particular, the proposed method uses the orthogonality of the encoded sets of symbols generated by different random seeds. In this way, portions of the information can be disseminated even if this has not been decoded yet. In fact, an easy management of the communication of these sets among nodes enhances the reliability of the communication as well as the speed of the information dissemination. In this work, we present the idea of this innovative approach and we provide results that show the advantages of using it over other solutions.

In this paper, we propose a novel TCP congestion control algorithm, named TCP SPC, which improves upon the performance of TCP Reno in wireless networks. TCP SPC exploits statistic process control (SPC) methods that have been used effectively in a variety of monitoring and control applications other than TCP. A TCP SPC sender uses RTT statistics to judge the network status, whereby the congestion window can be adjusted more intelligently. Comparing with conventional TCP, TCP SPC is more robust to sporadic losses due to wireless channel errors. Such errors often cause conventional TCP to over react, leading to unnecessary congestion window reduction. TCP SPC controls the congestion window in a way that is completely transparent to intermediate nodes and the destination. Therefore, it is compatible with any TCP implementation at the destinations. In this paper, we introduce TCP SPC and its implementation in a simulation environment. The simulation results show that TCP SPC can significantly improve throughput and fairness, especially in wireless networks with high-error links.

In this paper, we address the problem of how TCP sessions ramp up their transmission windows in a controlled way. We introduce a conservative slow start scheme that reduces to the regular slow start when session path queues are empty, but slows down the control window increase speed as buffers start to build up. We show via event driven simulation and open source based high speed experimental testbed the effectiveness of our conservative slow start mechanism in reducing packet losses and consequent retransmissions.

In this paper, we present the design, implementation and evaluation of a new TCP protocol, TCP-AW (TCP adaptive Westwood). This study was motivated by the intent to address simultaneously several challenging network scenarios, including high bandwidth efficiency in long and fat pipes, RTT fairness, and friendliness to legacy protocol, in a single protocol. TCP-AW leverages the key features of TCP Westwood and TCP adaptive Reno, namely, eligible rate estimation and delay- based adaptive AIMD parameter tuning, respectively. Extensive simulation and measurement results show that TCP AW yields good utilization of available bandwidth and achieves better RTT fairness. As for coexistence with TCP-NewReno, our major safety objective, was that new protocol compares more favorably than other promising protocols such as Hamilton-TCP, CUBIC and Compound-TCP. In contrast to other proposals, TCP-AW has no notions of small and large bandwidth delay product, instead, it scale seamlessly from current Internet paths to faster long distance paths.

Mobile wireless networks with intermittent connectivity, often called Delay/Disruption Tolerant Networks (DTNs), have recently received a lot of attention because of their applicability in various applications, including multicasting. To overcome intermittent connectivity, DTN routing protocols utilize mobility-assist routing by letting the nodes carry and forward the data. In this paper, we study the scalability of DTN multicast routing. As Gupta and Kumar showed that unicast routing is not scalable, recent reports on multicast routing also showed that the use of a multicast tree results in a poor scaling behavior. However, Grossglauser and Tse showed that in delay tolerant applications, the unicast routing overhead can be relaxed using the two-hop relay routing where a source forwards packets to relay nodes and the relay nodes in turn deliver packets to the destination via “mobility,” thus achieving a perfect scaling behavior of Θ(1). Inspired by this result, we seek to improve the throughput bound of wireless multicast in a delay tolerant setting using mobility-assist routing. To this end, we propose RelayCast, a routing scheme that extends the two-hop relay algorithm in the multicast scenario. Given that there are nssources each of which is associated with ndrandom destinations, our results show that RelayCast can achieve the throughput upper bound of Θ(min(1, n/nsnd)). We also analyze the impact of various network parameters and routing strategies (such as buffer size, multi-user diversity among multicast receivers, and delay constraints) on the throughput and delay scaling properties of RelayCast. Finally, we validate our analytical results with a simulation study.

Underwater mobile acoustic sensor networks are promising tools for the exploration of the oceans. These networks require new robust solutions for fundamental issues such as: localization service for data tagging and networking protocols for communication. All these tasks are closely related with connectivity, coverage and deployment of the network. A realistic mobility model that can capture the physical movement of the sensor nodes with ocean currents gives better understanding on the above problems. In this paper, we propose a novel physically-inspired mobility model which is representative of underwater environments. We study how the model affects a range-based localization protocol, and its impact on the coverage and connectivity of the network under different deployment scenarios.

There has been growing interest in urban surveillance using vehicles that monitor the environment, classify the events, e.g., license plate reading, and exchange metadata with neighbors in a peer-to-peer fashion. The idea is to create a totally distributed index of all the events, to be accessed by users. For instance, the Department of Transportation extracts traffic congestion statistics; the Department of Health monitors pollutants, and; the Police carries out forensic investigations. Mobile, vehicular sensing differs significantly from fixed (wireless) sensing. The vehicles have no strict limits on battery life, processing power and storage capabilities. Moreover they can generate an enormous volume of data, making current sensor harvesting solutions inadequate. In this talk we describes MobEyes, a middleware solution that diffuses data summaries to create a distributed index of the massive sensed data base. We discuss the challenges of designing and maintain such a system, from information dissemination to harvesting, routing and security.

Multicast streaming is gaining increasing importance in wireless ad hoc networks, in part because ad hoc scenarios often include team activities and the requirement for distribution of audio, video and situation awareness to the members. At the network level, techniques for routing the multimedia streams are quite mature. Much more challenging is the allocation of resources, the fair sharing among streams and the control of congestion.

As network topologies have grown in size and complexity, it is becoming a daunting task for network administrators to keep track the capacity dimensioning of newly installed web-servers within a single or multiple providers. In fact, monitor capacity dimensioning is not a trivial activity since network state changes rather frequently, in particular, in academic environments. In this paper, we describe estimation algorithms and the software architecture of an efficient network management suite to automatically mine path capacity and minimum delays from a venture point to a set of observed web servers. The principle of the suite is based on packet dispersion techniques and repetitive non-intrusive measurements. We provide analytical insights, simulation results and some real case studies where we argument about the correctness, accuracy and usefulness of the suite in the context of management and operation of complex IP based networks.

Vehicular networks create a new communication paradigm that enables to exploit the movement of cars to disseminate content. If network coding is used, vehicles have much more flexibility in content sharing and the system stability and scalability are promoted also in presence of mobility. Along this line, we propose an efficient mechanism to provide secrecy of the information. Traditional approaches based on encryption decrease the cooperation willingness of intermediate nodes, which have no expectation of recovering the file. Our scheme is based on obfuscation by processing and polluting the original file so that only the intended recipients, informed of corrupted blocks, can recover the information timely. We present several alternatives to efficiently provide weak secrecy and to foster cooperation. We simulate the file distribution in a vehicular network and show that the proposed scheme enhances content distribution in term of downloading speed and it is much more efficient than the ones that use encryption.

Highways are an essential component of our society because they are critical to quality of life and to local and national economies. Under good conditions, highways provide a safe and efficient route for people and goods to reach their destinations. However, as a direct consequence of their use, traffic congestion is ever-increasing, undermining the ability of highways to adequately provide an acceptable quality of service. It has become imperative for highway traffic to provide the same time guarantee quality as other transportation methods such as air and rail travel, while maintaining the convenience of flexible scheduling and destination for the individual traveler. In this position paper, we propose Active Highways, a fundamental departure from todaypsilas highway traffic management approaches that shifts the highway paradigm from a transportation infrastructure that monitors and controls traffic at the aggregate level, to a computer-based service that operates at the level of individual vehicles. In this sense, highways will become active managers of their own traffic similar to air traffic control. In our vision, future highways and future vehicles will communicate with one another, making the highway system aware of the driverspsila travel plans and allowing it to cooperate with and actively instruct the driver on achieving them. In particular, Active Highways will allow drivers to reserve slots in special high-priority intelligent lanes. This fine-grained traffic management model will guarantee travel time bounds, handle exceptions and enforce global community and environmental policies using real-time information from vehicle- and infrastructure-based sensors.

Besides safe navigation (e.g., warning of approaching vehicles), car to car communications will enable a host of new applications, ranging from offlce-on-the-wheel support to entertainment. One of the most promising applications is content distribution among drivers such as multi-media files and software updates. Content distribution in vehicular networks is a challenge due to network dynamics and high mobility, yet network coding was shown to efficiently handle such dynamics and to considerably enhance performance. This paper provides an in-depth analysis of implementation issues of network coding in vehicular networks. To this end, we consider general resource constraints (e.g., CPU, disk, memory) besides bandwidth, that are likely to impact the encoding and storage management operations required by network coding. We develop an abstract model of the network coding procedures and implement it in the wireless network simulator to evaluate the impact of limited resources. We then propose schemes that considerably improve the use of such resources. Our model and extensive simulation results show that network coding parameters must be carefully configured by taking resource constraints into account.

C-VeT's backbone is based on the UCLA's IEEE 802.11 campus-wide wireless infrastructure and is complemented by a wireless mesh provided by MobiMesh. The nodes participating in the mesh are installed in strategic campus location and perform packet routing as well as serve as access points for the mobile nodes. The mesh core network is deployed using IEEE 802.11a interfaces at 5.9 GHz and directional antennas while the access service is offered using IEEE 802.11g interfaces in the 2.4 GHz band. The network management and monitoring infrastructure has been deployed using a wide area wireless network technology in the ISM band of 900 MHz red links. The 900 MHz digital radio, provides enough bandwidth to perform realtime monitoring of the vehicular network and maintenance of the network nodes. The 900 MHz wireless infrastructure has been laid down to guarantee an independent channel to be used for network management and monitoring operations without interferences with on going experiments.

In this paper, we introduce a routing solution called "landmark overlays for urban vehicular routing environments" (LOUVRE), an approach that efficiently builds a landmark overlay network on top of an urban topology. We define urban junctions as overlay nodes and create an overlay link if and only if the traffic density of the underlying network guarantees the multi-hop vehicular routing between the two overlay nodes. LOUVRE contains a distributed traffic density estimation scheme which is used to evaluate the existence of an overlay link. Then, efficient routing is performed on the overlay network, guaranteeing a correct delivery of each packet. We evaluate LOUVRE against the benchmark routing protocols of GPSR and GPCR and show that LOUVRE performs higher in packet delivery and achieves lower hop count.

Several diseases and medical conditions require constant monitoring of physiological signals and vital signs on daily bases, such as diabetics, hypertension and etc. In order to make these patients capable of living their daily life it is necessary to provide a platform and infrastructure that allows the constant collection of physiological data even when the patient is not inside of the coverage area. The data must be rapidly "transported" to care givers or to the designated medical enterprise. The problem is particularly severe in case of emergencies (e.g. natural disasters or hostile attacks) when the communications infrastructure (e.g. cellular telephony, WiFi public access, etc) has failed or is totally congested. In this paper we present an evaluation of of the vehicular ad-hoc networks (VANET) as an alternate method of collecting patient pre-recorded physiological data and at the same time reconfiguring patient medical wearable body vests to select the data specifically requested by the physicians. Another important use of vehicular collection of medical data from body vests is prompted by the need to correlate pedestrian reaction to vehicular traffic hazards such as chemical and noise pollution and traffic congestion. The vehicles collect noise, chemical and traffic samples and can directly correlate with the "stress level" of volunteers.

The interests in health care have considerably increased these days as the aging population becomes larger. Health care has grown to the one of most active research areas especially in the area of wireless, mobile health monitoring systems. The wireless network technologies have advanced to the point where they can enable and help deploy a very broad gamut of systems suitable for medical applications. Several researches have proposed to replace the wired connections among medical devices with wireless connections. Wireless network technologies interwork with sensor equipped BodyLANs. Wireless personal area networks (WPANs) are well positioned to support health care applications in limited geographic areas. In particular, the characteristics of Bluetooth and its popularity make it the preferred network infrastructure for HealthNet environments. However, Bluetooth has the "bad reputation" of long connection delays, which may be disastrous in some health applications. In this paper we address the connection delay and propose a new data transfer protocol based on Bluetooth version 2.1. The 2.1 version was published very recently and offers new features that are interest to our application. Among the new features we leverage extended inquiry response (EIR) and secure simple pairing (SSP) to solve the delay problem. Extensive simulation results show that the proposed system significantly improves data delivery as well as power consumption. It solves a well known problem in Bluetooth based wireless networks. Using our proposed scheme, Bluetooth devices are now adequate to support sophisticated scenarios such as emergencies and urgent data dissemination requirements.

Remote medical monitoring with medical sensors and wireless communications has recently gained attention for the potential savings and improved quality in patient health-care. Currently, many mobile wireless medical infrastructures connect to the Internet in a point-to-point fashion, such as the cellular network. However, our research investigates new models for remote patient care that exploit P2P networking among patients and healthcare providers (nurses, doctors, emergency personnel). In this paper, we identify several medical applications based on P2P Health Networking focusing on two specific scenarios where nurses and patients are both equipped with Bluetooth devices. Nurses opportunistically collect, share and upload data in a P2P fashion. During an emergency, the nearest nurse is alerted via Bluetooth Enhanced Inquiry Response mechanism. The simulation and test-bed experimentation demonstrate that Bluetooth P2P networking is both feasible and cost-effective in remote medical monitoring.

We draw an analogy of biological cyanide poisoning to security attacks in self-organizing mobile ad hoc networks. When a circulatory system is treated as an enclosed network space, a hemoglobin is treated as a mobile node, and a hemoglobin binding with cyanide ion is treated as a compromised node (which cannot bind with oxygen to furnish its oxygen-transport function), we show how cyanide poisoning can reduce the probability of oxygen/message delivery to a "negligible" quantity. Like modern cryptography, security problem in our network-centric model is defined on the complexity-theoretic concept of "negligible", which is asymptotically sub-polynomial with respect to a pre-defined system parameter x. Intuitively, the parameter x is the key length n in modern cryptography, but is changed to the network scale, or the number of network nodes N, in our model. Based on this new analytic model, we show that RP (n-runs) complexity class with a virtual oracle can formally model the cyanide poisoning phenomenon and similar network threats. This new analytic approach leads to a new view of biological threats from the perspective of network security and complexity theoretic study.

Abstract — As the technology available on cars is increasing, a wide range of applications, from safety to entertainment, are becoming factually accessible to passengers. Many of these applications involves a one-to-many transmission model where a single car broadcasts a message that has to be forwarded, even with multiple hops, in a very short time to all the other cars located within a range of few kilometers from the source. Since the high mobility and density of a car network scenario, specific solutions need to be devised to choreograph a fast-delivery multihop broadcast. To this aim, we developed a practical and efficient technique that allows cars to estimate their communication range with the help of a very limited message exchange and exploit this information to reduce the number of transmissions, as well as the hops to be traversed, and hence the time, required by a broadcasted message to reach all the cars following the sender within a certain distance.

Abstract — Real-time applications are going to play a major role in Vehicular Ad-hoc Networks (VANETs). In this context, nodes ’ IP addresses need to be automatically configured in a very small time and with a reduced need for re-configurations. Due to the very high mobility of vehicles, however, traditional mechanisms for address auto-configuration fail to perform well. Aimed at solving this problem, we propose a novel Leader-based scheme that exploits the topology of VANETs and a distributed DHCP service to guarantee fast and stable address configuration. Keywords: Ad-hoc networks, VANET, address configuration. I.

In this paper we propose PiggyCode, a network-coding based scheme specifically designed to enhance TCP performance over IEEE 802.11 multi-hop wireless networks. The root of this approach is a network coding module operating between the network and the MAC layer. Each node running PiggyCode encodes, whenever it is possible, TCP-DATA and TCP-ACK packets belonging to the same information flow. The coding approach is conceptually analogous to piggyback the TCP- ACK packet within the TCP-DATA packet, with the substantial difference that, by performing network coding operations, the actual packet size remains unchanged. The proposed scheme is simple and effective. It leverages the benefits of network coding in the wireless environment, to jointly reduce the overall number of transmissions on the channel and speed up the delivery process of TCP-ACK packets, thus achieving significant improvements in terms of TCP performance.

Successes and failures during rescue operations after hurricane Katrina and the Twin Towers attack demonstrated the importance of supporting first responders with adequate means to perform their operations in an effective and safe way. From a networking point of view, one of the main challenges is that of providing first responders with multimedia information about the emergency as soon as possible, even from a remote location. To this aim, we designed an inter-vehicular communication system able to quickly discover and transmit real time multimedia information from around a crisis area to approaching first responders' vehicles. As vehicular communications are highly variable in nature, we endowed our system with a transmission range estimator that is put to good use to reduce the number of hops that a video triggering message sent by a vehicle will experience to reach its destination. Experimental results demonstrate the efficacy of our scheme in reducing the message delivery time and the traffic generated.

The paper describes a measurement campaign recently carried out by University of Bologna (UoB), National Inter-University Consortium for Telecommunications-(CNIT) and University of California Los Angeles (UCLA), on the CNIT GEO Skyplex platform. The aim of the experiments is the performance assessment of a wide range of TCP enhancements on network environments that include a real GEO satellite link. Measurements were carried out by means of the integrated UoB-CNIT testbed, fully controlled by remote through a Web interface. Analysis of live experiments data confirm the challenges posed by GEO sat channels, and show a negative influence of the Skyplex BoD technique on TCP start-up performance. Among the TCP enhancements compared in the paper, best results are provided by TCP Hybla and TCP Westwood, with an advantage of the former in heterogeneous environments characterized by a high level of RTT unfairness.

Vehicular ad hoc networks (VANETs) are envisioned to provide us with numerous interesting services in the near future. One of the most promising applications is the dissemination of commercial advertisements via car-to-car communication. However, due to non-cooperative behavior of selfish nodes or even malicious ones in the real-world scenario, such vehicular advertisement system cannot be realized unless proper incentives and security mechanisms are taken into consideration. This paper presents Signature-Seeking Drive (SSD), a secure incentive framework for commercial ad dissemination in VANETs. Unlike currently proposed incentive systems, SSD does not rely on tamper-proof hardware or game theoretic approaches, but leverages a PKI (Public Key Infrastructure) to provide secure incentives for cooperative nodes. With a set of ad dissemination designs proposed, we demonstrate that our SSD is robust in both incentive and security perspectives.

ZigBee is popular for Wireless Sensor Network (WSN) devices because of its low power consumption, built-in security method and ratified specifications. With these features, it is also suitable to be used with medical sensor devices. Medical sensors in a human body self organize a ZigBee Personal Area Network (PAN). These PANs are interconnected and form a HealthNet. For the interconnection, a ZigBee PAN detects existence of another PAN with beacon detection or active channel scan. Different ZigBee interconnection schemes are used after detection. PAN bridge method uses special bridge node that works for different PANs with time division method. PAN merge method temporarily changes PAN coordinator's role as bridge node and merges two PANs. Peer-to-peer network temporarily share all resources when two PANs are met, but all PANs have to use the same channel and operate as an ad-hoc network. In this paper, we perform extensive evaluations using NS-2 simulations to compare PAN interconnection methods. Results show that the PAN bridge is the most useful method because it is not affected by router/node ratio and is applicable to different channel usages.

Underwater environment represents a challenging and promising application scenario for sensor networks. Due to hard constraints imposed by acoustic communications and to high power consumption of acoustic modems, in underwater sensor networks (USN) energy saving becomes even more critical than in traditional sensor networks. In this paper the authors propose delay-tolerant data dolphin (DDD), an approach to apply delay-tolerant networking in the resource-constrained underwater environment. DDD exploits the mobility of a small number of capable collector nodes (namely dolphins) to harvest information sensed by low power sensor devices, while saving sensor battery power. DDD avoids energy-expensive multi-hop relaying by requiring sensors to perform only one-hop transmissions when a dolphin is within their transmission range. The paper presents simulation results to evaluate the effectiveness of randomly moving dolphins for data collection.

Introducing node mobility into the network also introduces new anonymity threats. This important change of the concept of anonymity has recently attracted attentions in mobile wireless security research. This paper presents identity-free routing and on-demand routing as two design principles of anonymous routing in mobile ad hoc networks. We devise ANODR (ANonymous On-Demand Routing) as the needed anonymous routing scheme that is compliant with the design principles. Our security analysis and simulation study verify the effectiveness and efficiency of ANODR.

In this paper, we propose a two-tier overlay multicast architecture (TOMA) to provide scalable and efficient multicast support for various group communication applications. In TOMA, multicast service overlay network (MSON) is advocated as the backbone service domain, while end users in access domains form a number of small clusters, in which an application-layer multicast protocol is used for the communication between the clustered end users. TOMA is able to provide efficient resource utilization with less control overhead, especially for large-scale applications. It also alleviates the state scalability problem and simplifies multicast tree construction and maintenance when there are large numbers of groups in the network. To help MSON providers efficiently plan backbone service overlay, we suggest several provisioning algorithms to locate proxies, select overlay links, and allocate link bandwidth. Extensive simulation studies demonstrate the promising performance of TOMA

This paper studies the TCP performance with delayed ack in wireless networks (including ad hoc and WLANs) which use IEEE 802.11 MAC protocol as the underlying medium access control. Our analysis and simulations show that TCP throughput does not always benefit from an unrestricted delay policy. In fact, for a given topology and flow pattern, there exists an optimal delay window size at the receiver that produces best TCP throughput. If the window is set too small, the receiver generates too many acks and causes channel contention; on the other hand, if set the window too high, the bursty transmission at the sender triggered by large cumulative acks will induce interference and packet losses, thus degrading the throughout. In wireless networks, packet losses are also related to the length of TCP path; when traveling through a longer path, a packet is more likely to suffer interference. Therefore, path length is an important factor to consider when choosing appropriate delay window sizes. In this paper, we first propose an adaptive delayed ack mechanism which is suitable for ad hoc networks, then we propose a more general adaptive delayed ack scheme for ad hoc and hybrid networks. The simulated results show that our schemes can effectively improve TCP throughput by up to 30% in static networks, and provide more significant gain in mobile networks. The proposed schemes are simple and easy to deploy.

We demonstrate a seamless vertical handoff solution, called Universal Seamless Handoff Architecture (USHA). USHA is simple and requires minimal modification to the current Internet infrastructure. Therefore, it is instantly ready for realworld deployment. In this demonstration, we present USHA in two scenarios. Using video streaming applications, we demonstrate that USHA is able to successfully maintain the application connectivity and achieve almost zero delay during a vertical handoff. Moreover, we present a vertical handoff detection technique based on the end-to-end link capacity monitoring. The ongoing work of this study is to improve the accuracy of the handoff detection and to enhance application QoS support for vertical handoffs given the accurate handoff detection is provided.

Abstract — Ensuring fairness among players engaged in online games is a challenging task. Yet, it is a fundamental requirement that can make the difference between having customers that persist or desist in using this kind of application. Answering to this demand, we present here an event delivery mechanism among mirrored game servers able to effectively uplift the fairness degree during game sessions through the heterogenesis of ends in targeting interactivity. We also provide extensive results that sustain our claim.

In this demonstration, we will showcase SenProbe, a lightweight capacity estimation technique specifically designed for the CSMA based wireless sensor networks. SenProbe is a packet train technique based on the concept pioneer by CapProbe, but designed specially for the wireless environment. We will use wireless devices with limited radio ranges to display the properties of multi-hop wireless networks (a table top experiment). More specifically, we will illustrate wireless properties with IEEE 802.15.4 enabled devices, and offer insights into how the capacity of a wireless path changes in real wireless environments can be deployed, measured, and used. This tool will be useful for network users as well as network designers to gain better understanding of their network, and plan their activities accordingly. This demonstration aims to provide results that can be of assistance in various facets of IEEE 802.15.4 enabled intelligent home/industrial networking environments.

The current paper proposes a novel end-to-end congestion control suitable for multimedia flows, with the primary aim of guaranteeing a good level of smoothness to the connections that employ it. The suggested strategy, termed Adaptive GAIMD, has as its starting point a blind, window-based scheme named General Additive Increase Multiplicative Decrease (GAIMD); it however enhances it through a measurement-based prediction of network conditions, based on the observation of the interarrival times of the most recently received triple duplicate acknowledgments. Such forecast allows the control to selectively switch to the AIMD policy, i.e., to a TCP-like behavior, when the network drifts towards overload conditions. On the other hand, if the network is sensed lightly loaded, the control behaves as GAIMD. In all cases, Adaptive GAIMD guarantees a smoother packet delivery than native GAIMD and TCP would. The validity of the proposed approach is experimentally proved, performing numerous tests and comparisons between Adaptive GAIMD, GAIMD and TCP-Sack, that took place on a geographical link spanning from Modena, Italy, to Los Angeles, United States.

With the increasingly deployed Wireless Personal Area Network (WPAN) devices, channel conflict has become very frequent and severe when one WPAN technology coexists with other WPAN technologies in the same interfering range. In this paper, we study the coexistence issue between various IEEE 802.15 based WPAN technologies. We present analytical models on the non-conflicting channel allocation probabilities, focusing on the coexistence scenarios of one WPAN technology coexisting with another. The results show that channel allocation conflicts occurs frequently in all cases, and is especially severe between IEEE 802.15.3 and IEEE 802.15.4 networks. On the other hand, the probability of non-conflict channel allocation is less dramatic between a single IEEE 802.15.1 and coexisting IEEE 802.15.4 networks. In addition, the proposed models in this paper are also applicable to other wireless technologies, as long as the channel allocation mechanisms are known.

In this paper we enhance the Digital Content Mediator (DCM) approach, a legitimate online service that uses financial incentives as an effective weapon to fight against online piracy. We provide needed network security support for the DCM service. The DCM mediator is a trusted notary to ensure fair and legitimate deals between digital content selling peers and buying peers. (1) In our design, the mediator sees no raw bits of digital contents. This saves storage and communication resource for the central mediator. (2) For the seller and buyer in a DCM-legitimized transaction, one wants payment and the other wants the content. The DCM protocol ensures that neither of them can stop the protocol in the middle to steal its service without serving the other party. (3) A digital content may have many legitimate copies from large amount of sellers. In a large-scale random network like the Internet, transaction fairness is defined as the condition that a buyer wants to buy the copy from the seller with shortest downloading delay (i.e., largest seller-to-buyer pairwise bandwidth) given the same amount of financial charge. DCM employs flow network security countermeasures to ensure that a seller keeps its bandwidth promises. Our experiments on the Internet confirm the effectiveness of our design.

In this paper we study multi-hop ad hoc routing in a Underwater Sensor Network (UWSN), a novel network paradigm for ad hoc underwater investigation with a large number of low cost underwater sensors. In UWSN, sensors are mobile with water current and dispersion, and use a wireless acoustic channel for communications. However, the large propagation latency and very low bandwidth of an acoustic channel could cause widespread collisions. Moreover, the mobility of sensors requires route management and causes additional traffic, thus worsening the situation. In this paper, we propose Under-Water Diffusion (UWD), a multi-hop ad hoc routing and in-network processing protocol. Since any on-demand flood or proactive exchange is considered harmful in underwater, UWD uses no proactive routing message exchange and negligible amount of ondemand floods in the environment with homogeneous GPSfree nodes and random node mobility. We validate UWD through both the mathematical analysis and simulations.

This paper presents AODV-DFR, a hybrid routing scheme that gracefully integrates the characteristics of on-demand and proactive routings. AODV-DFR shows great scalability for mobility and traffic load. We have demonstrated that AODV-DFR outperforms on-demand routing protocols (such as AODV), georoutings (such as GPSR) and adaptive hybrid routing protocols (such as ADV) in high mobility and traffic load. The improvement is more significant with higher mobility and traffic load. AODV-DFR sustains high packet delivery rates far beyond the saturating points for other routing protocols

Mobile ad-hoc networks (MANETs) are most useful in unprepared emergencies where critical applications must be launched quickly. However, they often operate in an adverse environment where end-to-end connectivity is highly susceptible to disruption. Adjusting the motion of existing nodes or deploying additional nodes can improve the connectivity under some circumstances, but for scenarios where connectivity cannot be immediately improved, disruption must be coped with properly. In this paper we propose the ad-hoc storage overlay system (ASOS). ASOS is a self-organized overlay of storage-abundant nodes to jointly provide distributed and reliable storage to data flows under disruption. ASOS is a delay-tolerant networking (DTN) approach that significantly improves the applicability of MANETs in practice

Over recent years, mobile Internet devices such as laptops, PDAs, smart phones etc, have become extremely popular and widespread. Once on board of a vehicle, these devices can automatically connect to the vehicle processor and thus greatly amplify the communications and processing capabilities available to the owner in a "pedestrian mode". We envision that this "amplification" opportunity will be one of the drivers of car to car and car to curb communications. In fact, the car communications system will not be used exclusively for mobile Internet access, but also as a distributed platform for the "opportunistic" cooperation among people with shared interests/goals. Exchanging safety messages among vehicles is a compelling example. Stretching opportunistic cooperation well beyond safety messages, we discuss in this paper the concept of virtual "flea market" over VANET called FleaNet In FleaNet, customers, either mobile (i.e., vehicles) or stationary (i.e., pedestrians, roadside shop owner), express their demands/offers, e.g., want to buy or sell an item, via radio queries. These queries are opportunistically disseminated exploiting in part the mobility of other customers in order to find the customer/vendor with matching needs/resources. In the paper we identify the key performance metrics, namely query resolution latency, scalability, and mobility. Based on the metrics, using models and simulation, we show that FleaNet can efficiently support a market place over vehicular networks

Based on the IEEE 802.15.4 LR-WPAN standard, the ZigBee standard has been proposed to interconnect simple, low rate, and battery powered wireless devices. The deployment of ZigBee networks is expected to facilitate numerous applications, such as home-appliance networks, home healthcare, medical monitoring, consumer electronics, and environmental sensors. An effective routing scheme in a ZigBee network is particularly important in that it is the key to achieve resource (e.g., bandwidth and energy) efficiency in ZigBee networks. Routing in a ZigBee network is not exactly the same as in a MANET. In particular, while full function devices (FFD) can serve as network coordinators or network routers, reduced function devices (RFD) can only associate and communicate with FFDs in a ZigBee network. Therefore, different from traditional MANET routing algorithms, which only take into account node mobility to figure out a best route to a given destination, node heterogeneity plays an important role in ZigBee network routing. In this paper, we perform extensive evaluation, using NS-2 simulator, to study the impact of node heterogeneity on ZigBee mesh network routing. The results show that the ZigBee mesh routing algorithm exhibits significant performance difference when the network is highly heterogenous. We also reveal that the node type and the role of the node plays a critical role in deciding routing performances.

In a large scale Bluetooth network, scatternet is regarded as the only interconnection method among piconets. But, most Bluetooth devices do not support scatternet connection. Moreover, in high mobility situations, scatternet is not useful because of frequent disconnections and reconnections. We propose overlaid Bluetooth piconets (OBP) to interconnect piconets and form a virtual scatternet. Every piconet continuously changes its stages and collects metadata of piconets in the communication range. If metadata shows existence of data to transfer, an inter-piconet connection is made and data is transferred. We compared throughput and efficiency of OBP with those of scatternet. Results show the feasibility of OBP usage instead of scatternet

Multicast communication is an efficient means to support key network applications such as real-time teleconferencing and data dissemination. In this paper we devise a security architecture for multicast communications in mobile ad hoc networks (MANETs). Our design is both suitable in MANET environment and compliant to the IETF standard multicast group security architecture (MGSA). Because centralized servers are vulnerable to network dynamics and security attacks in a distributed MANET, we distribute the function of MGSA's group control key server (GCKS) to a dedicated subset of mobile backbone nodes in MANET. Unlike distributed GCKS nodes in stationary infrastructure networks, our GCKS backbone nodes are mobile, fully distributed and adaptive to network dynamics, in particular the constant and instant changes in network topology, node density and node mobility. We study the characteristics of our GCKS backbone design and its impacts on ad-hoc multicast security research. Our simulation study and Linux implementation confirm the effectiveness of the new MANET MGSA design

Mobile ad hoc networks require anonymous communications in order to thwart new wireless passive attacks; and to protect new assets of information such as nodes' locations, motion patterns, network topology and traffic patterns in addition to conventional identity and message privacy. In particular, in wireless ad hoc networks mobile nodes must rely on ad hoc routing to keep network functional for communication. The transmitted routing messages and cached active routing entries leave plenty of opportunities for eavesdroppers. To address the new challenges, several anonymous routing schemes have been proposed recently. However, in various network scenarios, how the different cryptographic operations impact the routing performance remains unclear. In this paper we investigate the impact from cryptographic operations needed for the anonymous features. The overhead considered includes both increased control packet size and prolonged processing delay. The protocols taken into account include ANODR, AnonDSR, ASR, MASK, and SDAR. We present results based on extensive simulation study. We use the standard/unprotected on-demand scheme AODV in the comparison to show how much cost is paid by each anonymous on-demand scheme. Our simulation study shows that various design choices in anonymous routing indeed trade performance with anonymity protection. We conclude that extensive performance study is needed to evaluate the practicality of any enhancement of these proposed schemes and any new anonymous routing schemes

IEEE 802.15.4 is an emerging wireless standard addressing the needs of low-rate wireless personal area networks with a focus on enabling various pervasive and ubiquitous applications that require interactions with our surrounding environments. In view of the application potential of IEEE 802.15.4, knowing the fundamental network properties soon becomes essential in fasten the interactivity between these devices. Among all, knowing effective capacity of a path in wireless networks is of particular importance in routing and traffic management. In this paper, we implement SenProbe, a recently proposed path capacity estimation tool specially designed for the multi-hop ad hoc wireless environment. We present an implementation of SenProbe in sensor operating system (SOS), and evaluate the behavior/effectiveness of SenProbe in various testbed setups; including an interfered setting that cannot be simulated. Experiment results validate the workings of SenProbe and offer insights into how the capacity of a wireless path changes in real wireless environments. Our efforts provide a basis for realistic results that can be of assistance in activities such as capacity planning, protocol design, performance analysis, and etc

In this article we study a smooth and efficient transport protocol for real-time video over wireless networks. The proposed scheme, named the video transport protocol (VTP), has a new and unique end-to-end rate control mechanism that aims to avoid drastic rate fluctuations while maintaining friendliness to legacy protocols. VTP is also equipped with an achieved rate estimation scheme and a loss discrimination algorithm, both end-to-end, to cope with random errors in wireless networks efficiently. We show by analysis that VTP preserves most of the convergence properties of AIMD and converges to its fair share fast. VTP is compared to two recent TCP friendly rate control (TFRC) extensions, namely TFRC Wireless and MULTFRC, in wired-cum-wireless scenarios in Ns-2. Results show that VTP excels in all tested scenarios in terms of smoothness, fairness, and opportunistic friendliness. VTP is also implemented to work with a video camera and an H.263 video codec as part of our hybrid testbed, where its good performance as a transport layer protocol is confirmed by measurement results.

Abstract Privacy in mobile ad hoc networks has new semantics in addition to the conventional notions for infrastructure networks. Mobility enabled by wireless communication has significantly changed privacy issues and anonymity research in many ways. In particular, mobility requires ad hoc routing schemes to transmit messages frequently in an open wireless medium. The routing traffic facilitates adversaries in conducting various attacks threatening the network security and privacy. In this work, we focus on passive routing attacks. We present an extensive study on new anonymity threats and classify the corresponding security demands into three new categories: (1)venue anonymity; (2)privacy of ad hoc network topology; and (3)privacy of motion pattern. These new aspects are all introduced by mobility and left unaddressed in fixed infrastructure. This leads us to investigate new design principles. Our study suggests thaton‐demand routing,identity‐free routing, andneighborhood traffic mixingare better design choices to defend against the new anonymity threats in mobile networks. The paper also demonstrates through examples on the visualization of the mobile anonymity attacks and on the quantification of the effectiveness of the attacks. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract Network scalability is one of the critical challenges and requirements in routing protocols for ad hoc networks. This paper presents a novel scalable routing protocol called Geo‐LANMAR. The proposed protocol inherits the group motion support of landmark routing (LANMAR) and applies the geo‐routing concept to deliver packets efficiently. In this framework, the integration between geo‐coordinates and table‐driven IP addressing is introduced. There is also an integration of group management with geo‐forwarding and IP group management. Geo‐LANMAR uses link‐state propagation over a virtual topology built on landmarks, and a fisheye like scheme makes this propagation very efficient. The virtual topology helps recover from voids. For extra efficiency, a novel metric called effective traveled distance (ETD) allows us to predict voids or obstacles. With respect to LANMAR, Geo‐LANMAR reduces advertisement update overhead (O/H) and features robust forwarding. Consequently, Geo‐LANMAR is more scalable to large ad hoc networks with group motion. The performance evaluation of Geo‐LANMAR shows that Geo‐LANMAR gives high scalability for large networks in terms of control O/H, end‐to‐end delay, and packet delivery ratio as compared with other routing protocols such as AODV, LANMAR, and GPSR. Copyright © 2006 John Wiley & Sons, Ltd.

This paper presents a novel routing protocol called Geo-LANMAR. This routing scheme is able to get full advantages of group motion of mobile nodes to reduce the routing overhead and offer high network scalability. This protocol inherits same advantages of LANMAR protocol regarding the group motion support and its idea is to use the long-distance gee-forwarding for the extra-scope routing such as the terminodes routing and the optimized link-state routing (OLSR) for the intra-scope routing. Together the geo-routing forwarding scheme, a global update propagation scheme based on the hazy sighted link state routing (HSLS) between landmark nodes (cluster heads) is applied. An asymptotic analysis of Geo-LANMAR protocol is proposed and a rule that binds the intra-scope and extra-scope overhead cost is found. The novel routing scheme has been compared with the standard routing protocols such as AODV, GPSR and LANMAR.

A novel routing scheme called GeO-LANMAR routing has been proposed in this paper. This scheme combines the local link-state routing protocol until k-hop and a long-distance greedy forwarding. Geo-LANMAR supports group motion and gives high scalability for large network. It uses the concept of local group area (LGA) to define region where to forward data packets through geo-forwarding scheme. It makes usage of a virtual topology between LGAs and an optimized Hazy sighted link state (HSLS) link-state routing protocols. It combines the benefit of LANMAR protocol in terms of group motion support with the scalability of terminodes routing. A hybrid forwarding scheme (proactive and geo-routing) and a coarse topology knowledge through the HSLS protocol running between LGAs is applied. A performance evaluation of Geo-LANMAR vs. other routing protocols such as AODV, LANMAR and GPSR has been lead out.

TCP suffers from known problems in constrained environments such as satellite and wireless networks. And the problems grow more severe as networks grow increasingly integrated and diverse, where local optimization fail to suffice. One established method for dealing with these problems involves subdividing, or splitting the end-to-end TCP connection into a number of sub-connections. In this paper, we take an indepth look at the buffer requirements for "split connections". After briefly introducing the mechanics of a split connection, we proceed to identify a simple analytic model describing the behavior of the split connection and develop a number of design "rules of thumb" based on our analysis. We compare the results of simulations with the model and measure the efficacy of our design constraints, finding them to improve both the stability and performance of splitting. Finally, we discover that when used properly, oversubscribing, i.e., advertising non-existent space, may greatly reduce the required per-connection buffer-space in some situations.

In this work, we determine an analytical relationship between the average path length of traffic connections of a Bluetooth scatternet and the overall throughput and power consumption of the network. Results obtained implementing this analytical relationship to different scatternet topologies are presented and discussed. By reducing the hop count in a scatternet we can achieve better performance in terms of throughput and power consumption. Therefore, the issue of minimizing the hop count in the presence of mobility, changing traffic flows and varying interference receives an important role. In our analysis we also show the impact of the link quality on the overall throughput. The obtained results motivate the importance of heuristics aimed at reducing the communication path length in a scatternet.

Smart antennas present a radical way to improve the capacity of wireless networks. The advantages of such antennas can be leveraged by the MAC and higher layers. In this paper, we present SPACE-MAC, a MAC protocol which enables "spatial reuse" of the medium by multiple transmit/receive pairs which are in the same collision domain. SPACE-MAC prevents interference between such pairs by selectively nulling the signals from potentially interfering transmissions. This is achieved in a totally distributed fashion utilizing channel state information (CSI) at both transmitter and receiver to adjust antennas weights for each packet transmission. SPACE-MAC can operate effectively in cluttered (e.g., indoor) environments. SPACE-MAC achieves spatial reuse without requiring a separate channel for exchanging channel state information. This allows considerably better channel utilization. We investigate performance improvements of SPACE-MAC with respect to IEEE 802.11 DCF MAC using omnidirectional antennas.

In this paper, we propose a new version of TCP to improve (1) efficiency in wired-wireless combined networks with nonnegligible random packet losses, and also (2) friendliness to existing protocols, such as TCP-Reno. TCP-Westwood (TCPW) was proposed to improve efficiency in such networks; however, it is shown to be unfriendly to existing protocols under certain RTT and/or router buffer capacities. Since friendliness to existing protocols is one of the most important issues in a real network environment where different protocols coexist, we propose TCPW-BBE (TCPW with buffer and bandwidth estimation) to ensure the friendliness even under varying effective buffer capacities. Based on buffer capacity estimation mechanism, TCPW-BBE reacts more appropriately to a packet loss event, whether the loss is due to congestion or link errors. Simulation results show that TCPW-BBE maintains friendliness to TCP-Reno in networks for a broad range of buffer capacities, RTT, with/without RED routers, yet retaining the efficiency of the original TCPW.

Multicast solutions have been evolving from "bottom" to "top", i.e., from IP layer (called IP multicast) to application layer (referred to as application layer multicast). Recently, there are some new proposals (named as overlay multicast) using certain "infrastructure" (composed of proxies) in the middle. Although it is well accepted that application layer multicast and overlay multicast are easier to deploy while sacrificing bandwidth efficiency compared with IP multicast, little research has been done to systematically evaluate and compare their performance. In this paper, we conduct a comparative study of different types of multicast routing protocols. We first present a qualitative comparison of three types of protocols, and then we provide a quantitative study of four representative protocols, namely, PIM-SSM, NARADA, NICE, and POM by extensive simulations. Our studies will help to answer some of the most important questions, such as which way to go: top, bottom, or in the middle?.

Traditional IP multicast faces a serious state scalability problem when there are a large number of groups in the network. Recently, a novel approach called aggregated multicast was proposed [6], in which multiple groups share one delivery tree. A key problem in aggregated multicast is group-tree matching (i.e., assigning groups to trees). In this paper, we formally study the dynamic version of the group-tree matching problem. We propose a generic dynamic on-line algorithm (GDOA) and provide an approach to determine the upper bound on its performance. We quantitatively compare the performance of GDOA and other existing on-line heuristics. Extensive simulations demonstrate that GDOA is a very practical solution with promising performance and reasonable computation requirement.

Introducing node mobility into the network also introduces new anonymity threats. Nevertheless, this important change of the concept of anonymity has not been studied in state-of-art network security research. This paper presents the needed study. Then we show that anonymous routing in mobile networks has great impact on routing performance. We calls for the attention to devise new and efficient anonymous routing schemes for mobile ad hoc networks.

Real-time streaming over wireless links is challenging. The streaming protocol must be efficient and robust to random wireless loss, fair to itself, and friendly to legacy TCP. Various solutions have been proposed in the literature, among which the video transport protocol (VTP), TFRC wireless, and MULTFRC are end-to-end representatives. In this paper we provide an in-depth comparison on the performance of VTP, TFRC wireless, and MULTFRC in various wireless scenarios. The results show that VTP and TFRC wireless both perform well and deliver similar performance, with VTP exhibiting greater efficiency and smoothness in presence of heavy errors. In contrast, MULTFRC performs less satisfactorily, as it experiences large rate fluctuation and slow convergence caused by the frequent changes in the number of simultaneous connections.

Mobile ad hoc networks (MANETs) are vulnerable to routing attacks, especially attacks launched by non-cooperative (selfish or compromised) network members and appear to be protocol compliant. For instance, since packet loss is common in mobile wireless networks, the adversary can exploit this fact by hiding its malicious intents using compliant packet losses that appear to be caused by environmental reasons.In this paper we study two routing attacks that use non-cooperative network members and disguised packet losses to deplete ad hoc network resources and to reduce ad hoc routing performance. These two routing attacks have not been fully addressed in previous research. We propose the design of "self-healing community" to counter these two attacks. Our design exploits the redundancy in deployment which is typical of most ad hoc networks; Namely, it counters non-cooperative attacks using the probabilistic presence of nearby cooperative network members.To realize the new paradigm, we devise localized simple schemes to (re-)configure self-healing communities in spite of random node mobility. We develop a general analytic model to prove the effectiveness of our design. Then we implement our secure ad hoc routing protocols in simulation to verify the cost and overhead incurred by maintaining the communities. Our study confirms that the community-based security is a cost-effective strategy to make off-the-shelf ad hoc routing protocols secure.

Previous work analytically showed that communication path length reduction is an efficient way for improving the performance of Bluetooth scatternets. Maintaining short communication paths is mainly important in dynamic scatternets with changing traffic flows, mobile nodes and in the presence of interference, when the network topology changes continuously. In this work we aim at demonstrating through simulations that in such dynamic scatternets by periodically reducing the path length (i.e. hop count) between the communicating nodes, the overall throughput supported by the network can be significantly increased and the available energy of nodes can be consumed more efficiently. For this purpose, we present a distributed technique for repeatedly re-configuring the scatternet topology such that to support the current traffic flows between all of the communicating peers with a small number of hops.

Vertical handoffs between different wireless technologies usually lead to dramatic changes in the link capacity. A successful QoS solution for vertical handoffs must be able to fast track the capacity changes and agilely adapt the delivery rates and qualities of the ongoing applications. Though traditional AIMD-based source adaptation schemes (as found in TCP, TFRC, etc.) have been well designed for mild, gradual rate adjustments required by load fluctuations and network congestion, their response time is inadequate when the rate must be adjusted to the drastic network capacity changes that are typical in vertical handoff scenarios. To expedite the response to such changes, we propose in this paper two adaptive algorithms, named the fast rate adaptation (FRA) and early rate reduction (ERR), that are launched when the handoff is from low to high capacity (LOW-to-HIGH) or from high to low capacity (HIGH-to-LOW), respectively. We also propose two vertical handoff notification mechanisms to work with FRA and/or ERR, i.e. the implicit handoff notification (IHN) and explicit handoff notification (EHN). We show by simulation that our proposed schemes are able to provide better QoS support than the traditional AIMD based schemes during vertical handoffs.

Grido is an architecture that targets a network operator intending to provide enhanced services to its customers. This is achieved by setting up a "backbone" overlay network. A backbone overlay is a set of Internet hosts dedicated to providing overlay services. A network operator can view Grido as a sandbox for rapid prototyping and market adoption assessment of novel services. In the past, overlay networks have been designed to mitigate deployment issues of functionalities such as multicast and QoS at the network layer. Grido provides a WS-agreement based negotiation interface complying with the current Global Grid Forum (GGF) standards. We propose to use a novel virtual coordinates-assisted overlay construction and maintenance protocol. We demonstrate using simulations, that Grido incurs a low latency overhead while maintaining sparse connectivity on the backbone overlay. Grido also incurs low overhead for virtual coordinates estimation and chooses the closest 5% overlay node to any IP address, 95% of the time

In this paper, we propose a swarm intelligence strategy for constructing a mobile backbone multicasting network which leads to improved scalability and connectivity compared to conventional flat networks. The strategy combines a simple clustering technique and on demand multicast protocol (ODMRP). Also we show benefits of the mobile backbone network through a simulation study.

Abstract — In wireless ad-hoc networks, unidirectional links occur for several reasons: non uniform transmit power, non uniform background noise, and external interference. Several researchers have addressed unidirectional links and the associated unidirectional routing problem. The main focus has been so far on “unicast ” routing; the consensus is that unidirectional links should be detected and avoided. In this paper, we consider the multicast case and derive a different conclusion: namely, it pays to exploit unidirectional links rather then avoid them. To prove the point, we select a popular ad hoc multicast protocol, On-Demand Multicast Routing Protocol (ODMRP) and introduce a slightly modified version, ODMRP-ASYM, that can handle unidirectional links. Specifically, ODMRP-ASYM reroutes the Join Reply packet when a unidirectional link is detected on the Join Query path. The option is invoked only when a unidirectional link is detected. The main advantages are: control overhead comparable with ODMRP even in highly asymmetric topologies; virtually no performance degradation in presence of unidirectional links (while ODMRP typically suffers up to 15 % drop in delivery performance), and; 2-connectivity maintenance even if no bidirectional path exists between sender and receiver (in this case, unidirectional link avoidance strategies fail). Extensive simulation experiments demonstrate ODMRP-ASYM robustness to unidirectional links and superiority over conventional ODMRP.

Routing protocols for mobile ad-hoc networks have been evaluated extensively through simulation because various network conditions can be easily configured, tested, and replicated across different schemes in simulation than in a real system. Recently, some of these schemes have been implemented in academic, industry and defense testbeds. This gives researchers an opportunity to validate their simulation results with actual implementations. In this paper we report the lessons learned from the implementation of LANMAR (Pei et al. (2000)), a scalable routing protocol that was developed at UCLA as part of large-scale ad hoc network architecture for autonomous unattended agents under ONR support. LANMAR is designed to provide efficient, scalable routing in large ad-hoc wireless networks that exhibit group mobility. In this paper we describe the implementation of this protocol in Linux environments and report on experimental results based on this implementation. The results and lessons from these experiments have enriched our understanding of the LANMAR protocol and its interaction with the other layers and the environment, paving the way to protocol refinements and more efficient implementations.

Transmission control protocol Westwood (TCPW) has been shown to provide significant performance improvement over high-speed heterogeneous networks. The key idea of TCPW is to use eligible rate estimation (ERE) methods to intelligently set the congestion window (cwnd) and slow-start threshold (ssthresh) after a packet loss. ERE is defined as the efficient transmission rate eligible for a sender to achieve high utilization and be friendly to other TCP variants. This work presents TCP Westwood with agile probing (TCPW-A), a sender-side only enhancement of TCPW, that deals well with highly dynamic bandwidth, large propagation time/bandwidth, and random loss in the current and future heterogeneous Internet. TCPW-A achieves this goal by adding the following two mechanisms to TCPW. 1) When a connection initially begins or restarts after a timeout, instead of exponentially expanding cwnd to an arbitrary preset sthresh and then going into linear increase, TCPW-A uses agile probing, a mechanism that repeatedly resets ssthresh based on ERE and forces cwnd into an exponential climb each time. The result is fast convergence to a more appropriate ssthresh value. 2) In congestion avoidance, TCPW-A invokes agile probing upon detection of persistent extra bandwidth via a scheme we call persistent noncongestion detection (PNCD). While in congestion avoidance, agile probing is actually invoked under the following conditions: a) a large amount of bandwidth that suddenly becomes available due to change in network conditions; b) random loss during slow-start that causes the connection to prematurely exit the slow-start phase. Experimental results, both in ns-2 simulation and lab measurements using actual protocols implementation, show that TCPW-A can significantly improve link utilization over a wide range of bandwidth, propagation delay, and dynamic network loading.

This paper studies TCP performance in a stationary multihop wireless network using IEEE 802.11 for channel access control. We first show that, given a specific network topology and flow patterns, there exists an optimal window size W* at which TCP achieves the highest throughput via maximum spatial reuse of the shared wireless channel. However, TCP grows its window size much larger than W* leading to throughput reduction. We then explain the TCP throughput decrease using our observations and analysis of the packet loss in an overloaded multihop wireless network. We find out that the network overload is typically first signified by packet drops due to wireless link-layer contention, rather than buffer overflow-induced losses observed in the wired Internet. As the offered load increases, the probability of packet drops due to link contention also increases, and eventually saturates. Unfortunately the link-layer drop probability is insufficient to keep the TCP window size around W'*. We model and analyze the link contention behavior, based on which we propose link RED that fine-tunes the link-layer packet dropping probability to stabilize the TCP window size around W*. We further devise adaptive pacing to better coordinate channel access along the packet forwarding path. Our simulations demonstrate 5 to 30 percent improvement of TCP throughput using the proposed two techniques.

TCP throughput limitations over wireless links have received considerable attention in the last few years. One of the problems is that TCP congestion control interprets packet losses as an indication of congestion, whereas in wireless links, losses could be due to transient link quality degradations. In this paper, we propose and study a link layer solution and evaluate its effects on TCP in the context of Bluetooth. We enhance the Bluetooth link layer to make use of channel state information and accordingly adapt the Bluetooth packet type to enhance TCP throughput We propose a simple analytical method to determine the optimal packet type for a given channel state by adding FEC support or changing packet size. Since wireless interfaces, such as 802.11 or Bluetooth, can provide information regarding the channel state using relevant APIs, this simple enhancement can easily be added to the link layer. We implemented this functionality in the Bluetooth link layer. Our simulation experiments show that the proposed adaptive packet type solution significantly improves TCP throughput. The throughput enhancement increases with the error rate. For high error rates close to 0.1%, the link layer enhanced with the adaptive scheme is able to maintain good TCP throughput, whereas throughput is almost zero when the adaptive scheme is not used.

The maturing distributed file sharing technology implemented by Napster has first enabled the dissemination of musical content in digital forms, permitting to costumers an ubiquitous reach to stored music files from around the world. In the post-Napster era, the Apple iTunes online music service has hit a record share of 16.7% in the MP3 player market. This is only the most prominent example of the success of digital music distribution based on packet network technologies. However, to the best of our knowledge, the most noteworthy aspect of the success of digital music distribution is that little about this music delivery technology is really new. To deeply change the trend of this technology business, we claim that wireless technologies must come on the scene. In particular, the digital music delivery model may take benefit by the integration of the wired Internet with a plethora of several, alternative wireless technologies, such as, for example, WiFi, WPAN and 3G. In this challenging context, we have developed a wireless Internet application designed to support the distribution of digital music to handheld devices. The main novelty of our software application amounts to its ability in providing a seamless music delivery service even in the presence of horizontal and vertical handoffs. We have taken measurements from real-world experiments that show the efficacy of the system we have developed.

TCP westwood (TCPW) has been shown to provide significant performance improvement over high-speed heterogeneous networks. The key idea of TCPW is to use eligible rate estimation (ERE) methods, to set the congestion window (cwnd) and slow start threshold (ssthresh) after a packet loss. ERE is defined as the transmission rate a sender ought to use to achieve high utilization and remain friendly to other TCP variants. This paper presents TCP westwood with agile probing (TCPW-A), a sender-side only enhancement of TCPW. TCPW-A perform well when faced with highly dynamic bandwidth, large propagation time/bandwidth, and random loss in the current and future heterogeneous Internet. TCPW-A achieves its goal by incorporating the following, two mechanisms: 1) when a connection initially begins or re-starts after a timeout, instead of exponentially expanding cwnd to an arbitrary preset ssthresh and then going into linear increase. TCPW-A uses agile probing, a mechanism that repeatedly resets ssthresh based on ERE and forces cwnd into an exponential climb each time. The result is fast convergence to a more appropriate ssthresh value. 2) In congestion avoidance, TCPW-A invokes agile probing upon indication of unused extra bandwidth via a scheme we call load gauge (LG). Experimental results, both in Ns-2, and in measurements using FreeBSD implementation, show that TCPW-A can significantly improve link utilization over a wide range of bandwidth, propagation delay and dynamic network loading.

.4brtroct- Nest generation nehvorlis with large bandwidth and long drlay pose a major challenge to TCP performance, especially during the startup period. In this paper we evaluate the performance of TCP RenaiNcwrcno. Vegns and Hoe's modification in large bandwidth delay nrhvork. We propose n modified Slow-start mechanism, rnllcd Adaptive Start (Astart), to improve the startup performance in such networks. When a connection initially begins or re-starts after a coarse timrout,- Astart ndaptivcly and repentedly resets the Slow-start Threshold (suthreslr) based on an cligihlr sending I'iitr estimation mrchanisrn proposrd in TCP Westwond. By iidapting to network conditions during the startup phase. it wndw is able to grow the congestion window (ocnh fast without incurring risk of huNw owrflow and multiple Iossrs. Simulation rxpcrirncnts show that Astart can significantly improve the link utiliiation under various bandwidth, buNrr sur;~nd round-trip propagation timrs. The mrthud avoids both under-utiliriition dur to prrmature Slowstart termination, as wcll ils multiple I~XII~S due to initinlly setting srrlire.sli too high, or. increaing nmd tin) fiat. Experiments also show that Astart uchiews good fttirnrss rind fricndlincss toward TCP NewReno. Lab measuremrnts using a FrreBSD Astart implementation are also reported in this paper, providing futrhcr evidence of the gains nchirvahlr via Astart. Kqw-orr%r-congesrionn control;.sIow-.start; rate estimution. large bundwidth ddq nehvorks I.

Wireless communication is inherently vulnerable to errors from the dynamic wireless environment. Link layer packets discarded due to these errors impose a serious limitation on the maximum achievable throughput in the wireless channel. To enhance the overall throughput of wireless communication, it is necessary to have a link layer transmission scheme that is robust to the errors intrinsic to the wireless channel. To this end, we present interleaved-forward error correction (I-FEC), a clever link layer coding scheme that protects link layer data against random and busty errors. We examine the level of data protection provided by I-FEC against other popular schemes. We also simulate I-FEC in Bluetooth, and compare the TCP throughput result with Bluetooth's integrated FEC coding feature. We show that I-FEC consistently and significantly outperforms other link layer coding schemes by providing an impressive amount of protection against heavy channel burst errors.

Caching is a commonly used technique for reducing access latency and improving scalability. However, the static nature of existing network caching techniques makes them unsuitable for wireless environments. As mobile clients move from one location to another, the performance of these caches deteriorates. To combat this problem, object relocation strategies can be used, where objects are dynamically relocated to locations near the moving clients. Existing work on object relocation have focused on achieving relocation transparency. Little attention has been given to the network overhead introduced by the relocation. In this paper, we propose a low overhead object relocation strategy suitable for wireless environments. Object lists are passed between nodes prior to relocation to ensure only the nearest copy of each object is relocated. We have developed detailed analytical models of the proposed strategy and a number of other strategies to facilitate comparison. Analytical and simulation results show the proposed strategy effectively reduce the effect of mobility on the performance of network caches. The relocation overhead of the proposed method is also significantly lower compared to existing schemes.

CapProbe is an inexpensive and accurate means to estimate capacity. CapProbe combines both dispersion and end-to-end delay to estimate the capacity of the narrowest link on a path. We evaluate in this paper the accuracy of CapProbe estimation, and its dependence on end systems speed, packet sizes, narrow link speeds, and other system parameters. We test kernel and user level implementations of CapProbe and find the kernel implementation to be much more accurate. We also evaluate through experiments the effect of probing packet size on the accuracy of CapProbe estimation. Finally, we explore the idea of a "passive CapProbe" within the context of a TCP flow. Passive here means that the dispersion and delay observed for the TCP flow data and ACK packets, without introducing any additional probing packets. We test active and passive versions of CapProbe with TCP. The active version is found to produce more accurate capacity estimates than the passive version.

An end-to-end "foreground/background" priority scheme is useful for end hosts to utilize the residual capacity left unused by high-priority foreground applications. Several end-to-end prioritization schemes, such as TCP-LP (Low Priority) and TCP-Nice, have been proposed, however, the residual capacity cannot be fully utilized by these schemes. We propose TCP Westwood Low Priority (TCPW-LP), a scheme that maximizes the utilization of residual capacity without intrusion on coexisting foreground flows. TCPW-LP employs an "Early Window Reduction" mechanism to reduce its congestion window as a reaction to incipient congestion. To achieve high efficiency, the reaction is based on the estimation whether the congestion is caused by the foreground traffic or not. Simulation results show that TCPW-LP appropriately defers to foreground flows. Further, under a wide range of buffer capacity and link error losses, TCPW-LP better utilizes the residual capacity than other proposed priority schemes or even TCP Reno.

Low-rate TCP-targeted denial-of-service (DoS) attacks aim at the fact that most operating systems in use today have a common base TCP retransmission timeout (RTO) of 1 sec. An attacker injects periodic bursts of packets to fill the bottleneck queue and forces TCP connections to timeout with near-zero throughput. This work proposes randomization on TCP RTO as defense against such attacks. With RTO randomization, an attacker cannot predict the next TCP timeout and consequently cannot inject the burst at the exact instant. An analytic performance model on the throughput of randomized TCP is developed and validated. Simulation results show that randomization can effectively mitigate the impact of such DoS attacks while maintaining fairness and friendliness to other connections.

Video streaming has become a popular form of transferring video over the Internet. With the emergence of mobile computing needs, a successful video streaming solution demands 1) uninterrupted services even with the presence of mobility and 2) adaptive video delivery according to current link properties. We study the need and evaluate the performance of adaptive video streaming in vertical handoff scenarios. We use universal seamless handoff architecture (USHA) to create a seamless handoff environment, and use the video transfer protocol (VTP) to adapt video streaming rates according to "eligible rate estimates". Using testbed measurements experiments, we verify the importance of service adaptation, as well as show the improvement of user-perceived video quality, via adapting video streaming in the vertical handoffs.

We present a new capacity estimation technique, called CapProbe. CapProbe combines delay as well as dispersion measurements of packet pairs to filter out samples distorted by cross-traffic. CapProbe algorithms include convergence tests and convergence speed-up techniques by varying probing parameters. Our study of CapProbe includes a probability analysis to determine the time it takes CapProbe to converge on the average. Through simulations and measurements, we found CapProbe to be quick and accurate across a wide range of traffic scenarios. We also compared CapProbe with two previous well-known techniques, pathchar and pathrate. We found CapProbe to be much more accurate than pathchar and similar in accuracy to pathrate, while providing faster estimation than both. Another advantage of CapProbe is its lower computation cost, since no statistical post processing of probing data is required.

The problem of estimating the capacity of an Internet path is one of fundamental importance. Due to the multitude of potential applications, a large number of solutions have been proposed and evaluated. The proposed solutions so far have been successful in partially addressing the problem, but have suffered from being slow, obtrusive or inaccurate. In this work, we evaluate CapProbe, a low-cost and accurate end-to-end capacity estimation scheme that relies on packet dispersion techniques as well as end-to-end delays. The key observation that enabled the development of CapProbe is that both compression and expansion of packet pair dispersion are the result of queuing due to cross-traffic. By filtering out queuing effects from packet pair samples, CapProbe is able to estimate capacity accurately in most environments, with minimal processing and probing traffic overhead. In fact, the storage and processing requirements of CapProbe are orders of magnitude smaller than most of the previously proposed schemes. We tested CapProbe through simulation, Internet, Internet2 and wireless experiments. We found that CapProbe error percentage in capacity estimation was within 10% in almost all cases, and within 5% in most cases.

Several satellite systems currently in operation or under development claim to support broadband Internet applications. In these scenarios, transmission control protocol (TCP) plays a critical role. Unfortunately, when used with satellite links, TCP suffers from a number of well-known performance problems, especially for higher data rates and high altitude satellites with longer delays. In response to these difficulties, the satellite and Internet research communities have developed a large gamut of solutions ranging from architectural modifications to changes in the TCP protocol. Among these, one approach requiring minimal modifications involves splitting the TCP connection in two or more segments with one segment connecting terrestrial nodes across the satellite network. In this paper, we consider an evolution of this idea: placing a TCP proxy on board the satellite that further subdivides the end-to-end connection into separate TCP connections between ground and space. We focus upon the efficient use of buffer resources on board the satellite, while at the same time enhancing TCP performance. We evaluate two TCP protocol versions, TCP NewReno and TCP Westwood. We consider various geosynchronous earth orbit satellite scenarios, with and without the split proxy, and with different channel error conditions (random errors, shadowing, etc.). Using simulation, we show that an on-board proxy provides a number of distinct advantages and can enhance throughput up to threefold for both TCP New Reno and TCP Westwood, in some scenarios, with relatively modest on-board buffering requirements. The main contributions of this paper are: the on-board split proxy concept, the buffer management strategy, the use of a realistic "urban shadowing" model in the evaluation, and the extensive comparison of the recently announced TCP Westwood with the traditional TCP New Reno.

In this paper, we introduce a control theoretical analysis of the closed-loop congestion control problem in packet networks. The control theoretical approach is used in a proportional rate controller, where packets are admitted into the network in accordance with network buffer occupancy. A Smith Predictor is used to deal with large propagation delays, common to high speed backbone networks. The analytical approach leads to accurate predictions regarding both transients as well as steady-state behavior of buffers and input rates. Moreover, it exposes tradeoffs regarding buffer dimensioning, packet loss, and throughput.

The paper concerns TCP Westwood, a recently-developed modification of TCP, in combination with RED queue management. We develop a fluid-flow model of the protocol, and use it to study both equilibrium and dynamic features. On the equilibrium side, we identify the scaling of the congestion window with loss-probability, and compare it to TCP NewReno. We also use the model to find the boundary of stability, beyond which we see large oscillations; we find that the stable region of TCP Westwood is enhanced with respect to TCP NewReno. Furthermore we show preliminary evidence that oscillations, when they occur, have a limited impact on network throughput.

Today's emerging traffic is far removed from the traffic trends seen during the early days of Ethernet technology. As a result, the current IEEE 802.1 standards and its extensions to the spanning tree protocol fall short of providing satisfactory quality of service for traffic which has a significant amount of QoS-sensitive multimedia and VoIP traffic. In the current and near-future scenario of campus-wide networks with significantly large layer-2 clusters and numerous virtual LANs (VLANs), we show significant shortcomings of the basic spanning tree and the multiple spanning tree protocols with regard to QoS. We propose a novel, simple, and yet highly effective enhancement to the multiple spanning tree protocol to achieve a high degree of QoS by keeping in perspective the different characteristics of the various traffic types in the Diffserv framework. We discuss the problems of the current standards and present in detail our proposed extension to overcome them. Our simulation results show good improvements in throughput and significant benefits in delay for all classes of traffic to conclusively prove our claims.

Current traffic patterns are far removed from the traffic trends seen during the early days of Ethernet technology. Therefore, the current IEEE 802.1 standard and its extensions to the spanning tree protocol fall short of providing-satisfactory quality of service for traffic which has a significant amount of QoS-sensitive traffic. In addition, they do not provide a mechanism for stabilizing the traffic load among a whole bridged network where usually the root switch has to handle all the traffic from its child switches. In the current and near-future scenario of switching networks with significantly large layer-2 clusters and numerous VLANs, we show significant shortcomings of the basic spanning tree and the multiple spanning tree protocols with regard to QoS and load balancing. We propose to incorporate a bridge ID scheme of a regional root identifier which is used in multiple spanning tree instance (MSTI) to provide an efficient MSTI building method for QoS and load balancing. Through this scheme, the traffic source of a point-to-multipoint (P2MP) application can set itself as the root of MSTI satisfying the QoS constraint while roots of several regular MSTIs are built in a distributed way. We discuss the problem of building MSTI for P2MP applications and regular MSTIs and present in detail our proposed scheme. Our experiments for two cases show good improvement of QoS in terms of delay and load balancing of the whole bridge network.

Wireless links are error-prone. In next generation wireless networks, link capacities will still grow. It is known that in such configurations the performance of current TCP variants degrades severely. In this paper we propose a new transmission strategy for TCP in high error situations- bulk repeat (BR). We apply BR to TCP westwood (TCPW). BR has only three sender-side modifications to TCP, i.e. bulk retransmission, fixed retransmission timeout and intelligent window adjustment. BR permits efficient recovery from multiple losses in the same congestion window. To discriminate error from congestion loss, a loss discrimination algorithm (LDA), based on spike and rate gap threshold, is used. Simulation results in wireless network scenarios show that TCPW BR improves throughput performance up to an order of magnitude over TCPW and newreno when the error rate is high (>5%). The results also show that TCPW BR has satisfactory fairness and friendliness to TCP newreno.

IP multicast confronts a severe scalability problem when there are large numbers of multicast groups in the network due to state explosion and control explosion. In backbone networks, this state scalability problem is exacerbated, since there are potentially enormous multicast groups crossing backbone domains, in this paper, we propose a scalable protocol, called BEAM (bi-directional aggregate multicast), which uses the concept of aggregated multicast. BEAM is a distributed protocol using bi-directional trees. It is simple and easy to implement. Through simulations, we show that BEAM can greatly improve state scalability with very low overhead: up to 98% state and tree setup and maintenance overhead reduction with less than 0.14 bandwidth waste in our experiments.

Spatial diversity has been gaining significant momentum in cellular systems due to its ability to improve radio links in mobile wireless channels. Techniques of spatial diversity have been expanded to build foundations for advanced antenna array technology, to increase capacity in mobile wireless communication systems due to radiation patterns that direct energy only in the intended direction, thereby greatly reducing interference. Similar benefits may be gained in DSSS ad hoc networks, though work in this area has been limiter. To exploit spatial processing in future ad hoc networks, accurate array designs that embed spatial characteristics of the channel and radiation patterns are necessary to quantify the performance benefits. Therefore, in this study we designed a spatial diversity model and using simulation examined the performance benefits attained when configured in a DSSS as hoc network, subject to channels with narrowband and broadband interference.

Bluetooth "scatternets" are targeting wider geographical area applications in factories, warehouses, shopping malls and various sensor network applications. Though some earlier work has looked at scatternet formation and scheduling issues, less attention has been given to optimizing scatternet topologies. We consider in this paper topological design of scatternets, taking into consideration application traffic requirements. We study appropriate topologies, and size the network in terms of piconets. We develop a scatternet queuing model and use it to compare the delay-throughput characteristics of various topologies. We find that the best topology is application independent. The analytical model is also used to determine the optimal point to operate a scatternet, i.e., the traffic load that saturates the network. We validate all out analytical results by simulations.

Recent events show that distributed denial-of-service (DDoS) attack imposes great threat to availability of Internet services. In this paper, we study and evaluate DDoS attacks in a random flow network model, a novel and general approach to DDoS attack prevention and tolerance. The model can be used to evaluate the effectiveness of a DDoS countermeasure framework. Following the random flow network model and state-of-art Internet topology and traffic models, our simulation reveals that general relationship among several metrics derived from the model. Based on the simulation results, we suggest to build a more complete and effective DDoS countermeasure framework using complementary solutions to achieve DDoS attack detection, prevention, and tolerance at same time.

Efforts to provide connection oriented service over the inherently best-effort Internet started almost right after its birth. Today, there exist a multitude of solutions that have been proposed but have never been implemented due to their impracticability. We propose a practical solution for fast, low cost, scalable, and yet accurate QoS routing. We propose to use hierarchical approaches to make the scheme practical and cost-effective. At the same time, we increase network utilization and decrease inaccuracy of stale information by the use of multiple paths. An extensive simulation of the various permutations of schemes over a large set of topologies and traffic conditions validate the proposed schemes and prove conclusively that hierarchical schemes with multiple path capabilities not only result in significantly lower overhead, but also give high levels of QoS performance. This paper presents the architecture of our schemes, the multiple path computation algorithm, and the simulation results validating our claims.

In this paper, we investigate TCP performance over a multipath routing protocol. Multipath routing can improve the path availability in mobile environment. Thus, it has a great potential to improve TCP performance in ad hoc networks under mobility. Previous research on multipath routing mostly used UDP traffic for performance evaluation. When TCP is used, we find that most times, using multiple paths simultaneously may actually degrade TCP performance. This is partly due to frequent out-of-order packet delivery via different paths. We then test another multipath routing strategy called backup path routing. Under the backup path routing scheme, TCP is able to gain improvements against mobility. We then further study related issues to backup path routing, which can affect TCP performance. Some important discoveries are reported in the paper and simulation results show that by careful selection of the multipath routing strategies, we can improve TCP performance by more than 30% even under very high mobility.

Typical applications of mobile ad hoc networks (MANET) require group-oriented services. Digital battlefields and disaster relief operations make data dissemination and teleconferences a key application domain. Network-supported multicast is hence critical for efficient any-to-many communications. However, very little work has been done on "reliable" transport multicast. We propose and evaluate reliable adaptive lightweight multicast (RALM). The design choices of RALM are motivated by lessons we learned from evaluating the performance of traditional wired reliable multicast transport protocols (in particular, SRM) in ad hoc networks. We argue the two components, reliability and congestion control, are essential in designing a reliable multicast transport protocol for MANETs. RALM addresses both reliability and congestion control. It achieves reliability by guaranteeing data delivery to troubled receivers in a round-robin fashion. RALM's send-and-wait congestion control uses NACK feedback to adjust to congestion experienced by receivers. We show through simulations that RALM achieves perfect reliability while exhibiting low end-to-end delay and minimal control overhead compared against other protocols.

The blind flooding can become very inefficient because of redundant, "superfluous" forwarding. In fact, superfluous flooding increases link overhead and wireless medium congestion. In a large network, with heavy load, this extra overhead can have severe impact on performance and should be eliminated. Efficient flooding schemes to choose a dominant set of nodes have been recently proposed in ad hoc networks. In this paper, we compare the performance of a set of representative schemes via simulation using as criteria the flooding efficiency and the delivery ratio.

Streaming video as a form of media is becoming increasingly popular on the Internet. Real-time media such as video requires delay constraints from the network to ensure good quality at the receiver. While watching a video stream on his portable device connected to the Internet through the last-hop wireless link, the mobile user of tomorrow will expect a good experience. But, the time-varying nature of the wireless link can cause video frames to be dropped/delayed, affecting the quality of video at the receiver. In this paper, we propose a link layer approach to improve the quality of MPEG video streaming over a wireless link. We use Bluetooth as the wireless technology on which to test our scheme. Our results show that the quality of streaming video can be substantially improved with our scheme, particularly in bad channel conditions.

In this paper, we measure and model the distribution of multicast group members. Multicast research has traditionally been plagued by a lack of real data and an absence of a systematic simulation methodology. Although temporal group properties have received some attention, the location of group members has not been measured and modelled. However, the placement of members can have significant impact on the design and evaluation of multicast schemes and protocols as shown in previous studies. In our work, we identify properties of members that reflect their spatial clustering and the correlation among them (such as participation probability, and pairwise correlation). Then, we obtain values for these properties by monitoring the membership of network games and large audio-video broadcasts from IETF and NASA. Finally, we provide a comprehensive model that can generate realistic groups. We evaluate our model against the measured data with excellent results. A realistic group membership model can help us improve the effectiveness of simulations and guide the design of group-communication protocols.

This paper studies TCP performance over multihop wireless networks that use the IEEE 802.11 protocol as the access method. Our analysis and simulations show that, given a specific network topology and flow patterns, there exists a TCP window size W*, at which TCP achieves best throughput via improved spatial channel reuse. However, TCP does not operate around W*, and typically grows its average window size much larger; this leads to decreased throughput and increased packet loss. The TCP throughput reduction can be explained by its loss behavior. Our results show that network overload is mainly signified by wireless link contention in multihop wireless networks. As long as the buffer size at each node is reasonably large (say, larger than 10 packets), buffer overflow-induced packet loss is rare and packet drops due to link-layer contention dominate. Link-layer drops offer the first sign for network overload. We further show that multihop wireless links collectively exhibit graceful drop behavior: as the offered load increases, the link contention drop probability also increases, but saturates eventually. In general, the link drop probability is insufficient to stabilize the average TCP window size around W*. Consequently, TCP suffers from reduced throughput due to reduced spatial reuse. We further propose two techniques, link RED and adaptive pacing, through which we are able to improve TCP throughput by 5% to 30% in various simulated topologies. Some simulation results are also validated by real hardware experiments.

Significant TCP unfairness in ad hoc wireless networks has been reported during the past several years. This unfairness results from the nature of the shared wireless medium and location dependency. If we view a node and its interfering nodes to form a "neighborhood", the aggregate of local queues at these nodes represents the distributed queue for this neighborhood. However, this queue is not a FIFO queue. Flows sharing the queue have different, dynamically changing priorities determined by the topology and traffic patterns. Thus, they get different feedback in terms of packet loss rate and packet delay when congestion occurs. In wired networks, the Randomly Early Detection (RED) scheme was found to improve TCP fairness. In this paper, we show that the RED scheme does not work when running on individual queues in wireless nodes. We then propose a Neighborhood RED (NRED) scheme, which extends the RED concept to the distributed neighborhood queue. Simulation studies confirm that the NRED scheme can improve TCP unfairness substantially in ad hoc networks. Moreover, the NRED scheme acts at the network level, without MAC protocol modifications. This considerably simplifies its deployment.

Bluetooth is a low-cost, low-power technology initially intended as a replacement of cables between electronic devices. Bluettoth devices can form small network of up to 8 devices called piconets. The specification also defines networks of piconets called scatternets. Scatternets can have various uses such as for "monitoring" purposes in factories and warehouses or for ad hoc meetings. Scatternets require the use of a routing scheme to find paths in a dynamic network. Though considerable research has been done in the area of routing in ad hoc networks, the direct application of this may be inefficient to Bluetooth scatternets. Some previous work has also presented routing schemes for scatternets, but this does not present any results showing the performance of the routing scheme. In this paper, we present a routing scheme for Bluetooth scatternets, which is based on the zone routing protocol. We motivate the design of the routing scheme keeping in mind the specifics of the Bluetooth technology. We present simulation results for the scheme, which show that the scheme gives very low overhead while keeping the route acquisition latencies low. The routing information at a node does not require a large amount of storage. In fact, a parameter in the scheme can be varied to trade-off storage information and routing overhead versus route acquisition latency.

High capacity real-time data communications in sensor networks usually require multihop routing and ad hoc routing protocols. Unfortunately, ad hoc routing protocols usually do not scale well and cannot handle dense situations efficiently. These two issues-scalability and density-are the major limitations when we apply ad hoc routing schemes to sensor networks. Passive clustering (PC) classifies ad hoc/sensor nodes into critical and noncritical nodes without any extra transmission. By 2-b piggybacking and monitoring user traffic (e.g., data polling requests from a sink), PC deploys the clustering structure "for free". Moreover, PC makes even the first flooding as efficient as all subsequent floodings (i.e., no initialization overhead). PC introduces many benefits, including efficient flooding and density adaptation. As a result, PC reduces control overhead of ad hoc routing protocols significantly and, as a consequence, enables ad hoc routing in large, dense sensor networks. The resulting structure can be utilized in cluster-based ad hoc network/sensor networking as well as for active node selection.

Emerging wireless ad-hoc networks find their most important applications in untethered, mobile, multihop scenarios where there is no wired infrastructure. Yet, when the wired infrastructure (say, the Internet) is within reach, opportunistic connections to Internet sites may be established across the multihop network to transfer files and update databases. These file transfers use TCP for reliability and congestion control. Many believe that TCP should not be used in ad-hoc network due to it's inability to adapt to the high loss environment, but we believe that TCP will always have a part to play in wireless network in one form or another; studying the behavior of TCP will provide the direction for that adaptation. Recent experiments with ad-hoc, multihop 802.11 networks have exposed serious instabilities when TCP connections span both wired and wireless domains. In particular, some TCP connections capture the wireless channel and drive the throughput on other connections virtually to zero. This is most surprising in view of the fact that connections between 802.11 (single hop) wireless LAN stations and the Internet are well behaved, stable and fair. The problem of the unfairness compounds further when TCP connections have to share the bandwidth with in multihop ad-hoc network. In this paper, we present the issues regarding the wireless transport protocols by experimentally analyzing TCP performance.

IP multicast suffers from scalability problems as the number of concurrent active multicast groups increases, since it requires a router to keep a forwarding state for every multicast tree passing through it. In QoS multicast provisioning, the problem is exacerbated, since not only the forwarding state but also the resource requirement of a multicast group must be kept at the router. To provide scalable QoS multicast support, in this paper, we propose a novel architecture, called Aggregated QoS Multicast (AQoSM). Using the concept of aggregated multicast, AQoSM can support QoS multicast scalably and efficiently in DiffServ-supported MPLS networks. In this paper, we develop the framework for the architecture and provide a feasibility check from an implementation point of view. The architecture is flexible and can be customized to the needs and the existing protocols of a domain. Our simulations indicate that the architecture performs well in several common scenarios. It achieves smaller blocking of users with strong QoS requirements because of its load balancing capability. It also achieves up to 85% reduction in state with a modest 10% of bandwidth overhead.

Source specific multicast (SSM) is a viable solution for current multicast applications, since the driving applications to date are one to many, including Internet TV, distance learning, file distribution, streaming media, etc. It brings many benefits in billing, address allocation, and security. However, SSM still confronts the serious state scalability problem when there are a large number of simultaneous on-going multicast groups in the network. We propose a protocol to improve the state scalability of source specific multicast, which is called aggregated source specific multicast (ASSM). We design the detailed ASSM protocol and show that our solution can obtain significant multicast state and tree management overhead reduction while achieving transparency to end-users, compatibility with existing multicast technologies and low overhead.

This paper presents a cost-effective quality-of-service (QoS) routing scheme which deploys a heuristic algorithm to provision multiple QoS paths. Multiple QoS path provisioning is mainly aimed to provide reliable QoS guarantees for mission-critical applications. The proposed algorithm relaxes the strict disjoint path requirement and searches for more paths possibly less overlapped with each other and still satisfying given multiple QoS constraints. When multiple QoS paths are provisioned for the same destination, link/node failures become significantly less detrimental to ongoing QoS application traffic. The routing algorithm presented in this paper can be claimed to be cost-effective since a single iteration of the algorithm finds multiple QoS paths while previous research works require as many algorithm iterations as the number of searched QoS paths. This paper discusses the beneficial properties of the proposed algorithm, and simulation experiments present the reduced algorithm time complexity.

High errors and high delays create well-known problems with TCP. One established approach to solve this problem involves dividing TCP connections into segments, or splitting the connection. This paper takes this approach one step further by exploring the use of a TCP proxy on board a satellite for the purpose of enhancing end-to-end TCP performance. We show that this approach yields a number of important advantages, especially for small, mobile terminals, multi-segment systems, and multicast applications. As part of this architecture, we introduce a method of TCP backpressure using the advertised window, which optimizes memory usage on the satellite. Using simulation, we demonstrate that performance may improve by as much as three-fold.

TCP Westwood (TCPW) is a recently proposed sender side modification of TCP congestion control. TCPW relies an bandwidth share estimation techniques to enhance congestion control over high speed and/or wireless networks. The bandwidth share estimation methods turn out to be critical to guarantee both throughput improvement and friendliness towards widely used TCP protocols such as NewReno. In this paper we propose a new bandwidth share estimation technique, called "adaptive bandwidth share estimation", or ABSE. ABSE adapts to changing network congestion level, round trip times, and other relevant network conditions, as well as to the rate at which such changes occur. We compare the throughput gain and friendliness of ABSE with that of NewReno and previous estimation methods used for TCPW. We test the new technique using different simulation scenarios, including RED, to show the benefit of our proposed ABSE estimation method.

IEEE 802.11 MAC mainly relies on two techniques to combat interference: physical carrier sensing and RTS/CTS handshake (also known as "virtual carrier sensing"). Ideally, the RTS/CTS handshake can eliminate most interference. However, the effectiveness of RTS/CTS handshake is based on the assumption that hidden nodes are within transmission range of receivers. In this paper, we prove using analytic models that in ad hoc networks, such an assumption cannot hold due to the fact that power needed for interrupting a packet reception is much lower than that of delivering a packet successfully. Thus, the "virtual carrier sensing" implemented by RTS/CTS handshake cannot prevent all interference. Physical carrier sensing can complement this in some degree. However, since interference happens at receivers, while physical carrier sensing is detecting transmitters (the same problem causing the hidden terminal situation), physical carrier sensing cannot help much, unless a very large carrier sensing range is adopted, which is limited by the antenna sensitivity. We investigate how effective is the RTS/CTS handshake in terms of reducing interference. We show that in some situations, the interference range is much larger than transmission range, where RTS/CTS cannot function well. Then, a simple MAC layer scheme is proposed to solve this problem. Simulation results verify that our scheme can help IEEE 802.11 resolve most interference caused by large interference range.

In ad hoc, multihop wireless networks the routing protocol is key to efficient operation. The design of an ad hoc routing protocol is extremely challenging because of mobility, limited power, unpredictable radio channel behavior and constrained bandwidth. As the network grows large, two additional challenges must be faced: increasing node density, and large number of nodes. High density (i.e., a large number of neighbors within radio range) leads to "superfluous" forwarding of broadcast control messages. Large network size leads to large routing tables and high control traffic overhead. The two aspects are related and they both undermine the scalability of routing protocols. In this paper, we address scalability for a specific class of routing protocols, namely, proactive link state routing protocols. Link state protocols are desirable in many applications because of low access delay, ability to include QoS criteria in path selection, support of alternate routes, etc. Yet, these protocols are most affected by density and large scale. In the paper, we propose two techniques to overcome density and large scale, namely passive clustering and landmark routing. We compare via simulation our proposed solutions to other existing scalable schemes.

Bluetooth scatternets are formed by interconnecting Bluetooth piconets in an ad-hoc fashion and consists typically of the handheld electronic devices from one or more user(s). Thus, scatternets may be used to form and interconnect ad-hoc Bluetooth personal area networks (PANs). The inter-piconet Bluetooth units, i.e. the gateways interconnecting the piconets in a scatternet, need to time division multiplex their presence in each of their piconets. This requires an inter-piconet scheduling (IPS) algorithm, operating in each inter-piconet unit in order to efficiently coordinate its presence with other Bluetooth units. In this paper an IPS algorithm based on periodic rendezvous points is proposed and analyzed with simulations, The algorithm is called maximum distance rendezvous point (MDRP) and utilizes the Bluetooth SNIFF functionality to establish the periodic rendezvous points between gateways and their peer nodes. Simulation results show that TCP works well with MDRP, but the large round trip delays caused by the inter-piconet gateway nodes give a slowly growing flow control window for TCP. The latter will in particular have an impact on the TCP performance in scatternets hosting "thin" (embedded) clients with limited dynamic memory capacity.

Ubiquitous computing across a variety of wired and wireless connections still lacks an effective security architecture. In our research work, we address the specific issue of designing and building a security architecture for application session handoff, a functionality which we envision will be a key component enabling ubiquitous computing. Our architecture incorporates a number of proven approaches into the new context of ubiquitous computing. We employ the Bell-LaPadula (1976) and capability models to realise access control and adopt public key infrastructure (PKI)-based approaches to provide efficient and authenticated end-to-end security. To demonstrate the effectiveness of our design, we implemented an application enabled with this security architecture and showed that it incurred low latency.

A mobile ad hoc network (MANET) is usually assumed to be homogeneous, where each mobile node shares the same radio capacity. However, a homogeneous ad hoc network suffers from poor scalability. Recent research has demonstrated its performance bottleneck both theoretically and through simulation experiments and testbed measurement Building a physically hierarchical ad hoc network is a very promising way to achieve good scalability. In this paper, we present a design methodology to build a hierarchical large-scale ad hoc network using different types of radio capabilities at different layers. In such a structure, nodes are first dynamically grouped into multihop clusters. Each group elects a cluster-head to be a backbone node (BN). Then higher-level links are established to connect the BN into a backbone network. Following this method recursively, a multilevel hierarchical network can be established. Three critical issues are addressed in this paper. We first analyze the optimal number of BN for a layer in theory. Then, we propose a new stable clustering scheme to deploy the BN. Finally LANMAR routing is extended to operate the physical hierarchy efficiently. Simulation results using GloMoSim show that our proposed schemes achieve good performance.

The on-demand routing schemes in mobile ad hoc networks are appealing because of the lower routing overhead, compared with traditional proactive schemes. The on-demand routing protocols introduce routing overhead only in the presence of data packets that need routes. However, the control overhead of on-demand routing schemes increases with node geographic density and traffic pattern density. In fact, this is an undesirable feature for the scalable routing protocols whose control overhead should be under control to keep up with increasing offered load. As a solution for such a drawback of current reactive routing schemes, we propose the selective intermediate nodes mechanism. In this protocol, each node adaptively propagates routing information based on the local load level and cluster status. The local load level (local load status), based on channel utilization and queue size, reflects the load of the node in question and of all of its neighbors; the cluster status denotes the role of a node in a cluster (i.e., a cluster head, gateway or ordinary node). We demonstrate the effectiveness of our enhancement by applying it to ad hoc on-demand distance vector routing (AODV) and dynamic source routing (DSR). Simulation results show that the proposed idea significantly reduces the control overhead and improves the overall performance and scalability of the routing protocols.

TCP performance can be significantly affected when the buffer capacity at routers is small. This is possible when either many flows share the network or the bandwidth-delay product is large (e.g. satellite links). The behavior of various versions of TCP with respect to buffer capacity issues has not been studied in much detail. We investigate the behavior and performance of different TCP variants under small buffer capacity conditions. We recognize TCP pacing as a potential solution. However, instead of using TCP's sending rate as the dictating metric, we make use of the bandwidth-share estimate (BSE), maintained by TCP Westwood, to set the pacing interval. We call this newly proposed protocol paced-Westwood. We also show the need to scale BSE further to mitigate the effects of positive feedback in BSE. For this, we propose a further enhancement that we call /spl alpha/-paced Westwood that uses a scaling parameter /spl alpha/ to enforce convergence of BSE and the pacing interval. The proposed /spl alpha/-paced Westwood uses its BSE to space the packet bursts during the slow-start phase, resulting in a superior throughput in the troublesome low buffer capacity cases. With the help of simulations, we show that our enhanced TCP Westwood outperforms both unpaced as well as paced TCP NewReno under low buffer capacity networks.

The rapid advancement in wireless communication technology has spurred significant interest in the design and development of enhanced TCP protocols. Among them, TCP Westwood (TCPW) is a sender side only modification to improve TCP performance particularly over heterogeneous networks. The key idea of TCPW is to use rate estimation methods to set the congestion window and slow start threshold after a packet loss. When packet losses are not only due to buffer overflow, but random errors as well, TCPW estimation methods have been shown to provide significant performance improvement. The earliest estimation method, called bandwidth estimation (BE), however, may result in over-estimation under certain circumstances, and thus may be unfriendly toward non-TCPW traffic. TCPW CRB (combined rate and bandwidth estimation) and TCPW ABSE (adaptive bandwidth share estimation), have been later introduced to address this concern. The schemes provide better control of the tradeoffs among efficiency, friendliness, and implementation complexity. CRB may slightly sacrifice the efficiency gain to ensure friendliness. ABSE adaptivity mechanisms are more sophisticated and provide both better efficiency and friendliness.We summarize ABSE, which adapts to congestion level, as well as round drip time, and other network dynamics, thus providing enhanced and robust performance under various network conditions. Extensive experiments show that TCPW ABSE is able to enhance TCP performance significantly over "large leaky pipes", while maintaining friendliness toward TCP NewReno. We show that TCPW ABSE is robust to packet and ACK compression due to cross traffic on forward and backward paths. We also show that ABSE is robust to buffer size variations, which are inevitable in today's networks.

The standards that are supposed to play a leading role in third-generation mobile telecommunication and personal area networks in the near future are the Universal Mobile Telecommunication System (UMTS) and the Bluetooth (BT) radio technology, respectively. In this paper, we advocate that a hybrid architecture of UMTS and Bluetooth can take advantage of the complementary characteristics of these two technologies and provide a total solution for an indoor communication environment. We envision a cooperating scenario in which small Bluetooth networks (scatternets) offer basic wireless connectivity to several peripheral units scattered over small areas, while indoor UMTS supports communication among scatternets and provides wireless access to the Internet. We focus our analysis on a centralized topology, in which communication occurs only between the peripheral units and the access point. This topology can be used in many different application scenarios and represents an example of cooperation between 3G and PAN technologies. In addition to describing the architecture, we address the issue of fair capacity allocation in such a centralized topology and provide some analytic and simulation results for the topology considered.

Higher layer protocols in wireless networks need to dynamically adapt to observed network response. The common approach is that each session employs end-to-end monitoring to estimate quantities of interest, like delay, delay jitter and available bandwidth. A less conventional approach is to employ lower layer explicit feedback mechanisms in place or in aid of end-to-end efforts. Available bandwidth measurements are known to follow multi-modal distributions and therefore are especially difficult to measure and filter, even in wired networks. In 802.11-based multi-hop networks obtaining usable end-to-end measurements is questionable. They are affected by a combination of a large number of transient variables due to the virtual carrier sense, head of line problems on each link and mobility. Motivated by this, we are developing a network explicit feedback mechanism. Our study of this accurate network feedback architecture aids in the cost/benefit analysis of an important trade-off: deployment of network support mechanisms for transports and QoS, versus the simple, scalable and easily deployable end-to-end solution. We test our solution in: (i) multimedia adaptation and (ii) measurement based call admission. Loss rates of end-to-end adaptive video and audio connections have been more than 4 times higher than in the network feedback case. A simple call admission strategy has also proved very effective using the feedback. In our experiments it led the network to a maximal performance and stable operating point.

The use of contention-based MAC protocols combined with hidden terminal problems make multi-hop wireless ad hoc networks much more sensitive to load and congestion than wired networks or even wireless cellular networks. In such an environment, we argue that multicast reliability cannot be achieved solely by retransmission of lost packets as is typically done in wired networks with protocols such as SRM. We contend that in order to achieve reliable multicast delivery in such networks, besides reliability mechanisms, we must also consider jointly two components: reliability and congestion control. In this paper, we propose CALM, a congestion controlled, adaptive, lightweight multicast transport protocol and show that congestion control alone can significantly improve reliable packet delivery in ad hoc networks when compared to traditional "wired" reliable multicast protocols.

We propose a refinement of TCP Westwood which allows management of the efficiency/friendliness-to-NewReno tradeoff. We show that the refined TCP Westwood is able to achieve higher efficiency yet at the same time maintain friendliness. TCP Westwood (TCPW) implements a novel window congestion control algorithm based on available bandwidth estimation. The performance of TCPW has been promising, exceeding that of TCP NewReno in high speed and/or wired/wireless networks. However, under certain circumstances, TCP NewReno may experience some performance degradation because TCPW possesses more information and thus can take better advantage of available bandwidth. We propose combining the original TCPW sampling strategy that produces available bandwidth estimates (BE), with a new strategy that produces rate estimates (RE). Our studies show that RE works best when packet losses are mostly due to congestion. If on the other hand, the packet losses are mostly due to link errors, BE gives better performance. To achieve the "best of all worlds", we introduce a method we call combined rate and bandwidth estimation (CRB). A connection first infers the predominant cause of packet losses, and then uses the most appropriate estimation method. We also introduce the efficiency/friendliness tradeoff graph that provides better tradeoff visualization. In our experiments, we found that CRB provides a better compromise between efficiency and friendliness, and the means to manage such a tradeoff.

This paper suggests a new load aware routing (LWR) enhancement that improves on-demand routing protocols significantly in ad hoc networks. This paper describes deterministic characteristics of ad hoc networks and suggests improved routing strategies that can sustain the network functionality even under highly stressful data traffic. LWR evenly distributes the load throughout the networks. It also reduces redundant packet flooding which is major limitation of conventional ad hoc routing algorithms. Simulation results illustrate the performance improvements obtained with LRW by using new flooding control over conventional on-demand routings.

Abstract Secure communication is critical in military environments in which the network infrastructure is vulnerable to various attacks and compromises. A conventional centralized solution breaks down when the security servers are destroyed by the enemies. In this paper we design and evaluate a security framework for multilevel ad hoc wireless networks with unmanned aerial vehicles (UAVs). In battlefields, the framework adapts to the contingent damages on the network infrastructure. Depending on the availability of the network infrastructure, our design is composed of two modes. In infrastructure mode, security services, specifically the authentication services, are implemented on UAVs that feature low overhead and flexible managements. When the UAVs fail or are destroyed, our system seamlessly switches to infrastructureless mode, a backup mechanism that maintains comparable security services among the surviving units. In the infrastructureless mode, the security services are localized to each node's vicinity to comply with the ad hoc communication mechanism in the scenario. We study the instantiation of these two modes and the transitions between them. Our implementation and simulation measurements confirm the effectiveness of our design. Copyright © 2002 John Wiley & Sons, Ltd.

IP multicast suffers from a scalability problem with the number of concurrently active multicast groups because it requires a router to keep the forwarding state for every multicast tree passing through it and the number of forwarding entries grows with the number of groups. In this paper, we propose an approach to reduce the multicast forwarding state. In our approach, multiple groups are forced to share a single delivery tree. We discuss the advantages and some implementation issues of our approach, and conclude that it is feasible and promising. We then propose metrics to quantify state reduction and analyze the bounds on state reduction of our approach. Finally, we use simulations to verify our analytical bounds and quantify the state reduction. These initial simulation results suggest that our method can reduce multicast state significantly.

Group multicast refers to the kind of multicast in which every member of a group may transmit data to the group. Several QoS-aware routing algorithms for group multicast proposed previously take into account bandwidth requirement (which is the most important QoS metric to consider for many applications) and build source-based tree for each individual group member. Per-source tree approach has some advantages over shared-tree approach but suffers the drawbacks of higher control overhead and being less scalable especially with group size. In this paper we present an algorithm which builds shared tree for group multicast and can accommodate multiple QoS requirements including bandwidth and inter-member delay. Besides the advantages of having less control overhead and better scalability, our algorithm can support dynamic membership without recomputing the whole tree. The results from simulation experiments for multicast with bandwidth reservation show that our algorithm has similar performance in terms of tree cost and bandwidth utilization compared with two other per-source tree algorithms.

We study the performance of TCP Westwood (TCPW), a new TCP protocol with a sender-side modification of the window congestion control scheme. TCP Westwood controls the window using end-to-end rate estimation in a way that is totally transparent to routers and to the destination. Thus, it is compatible with any network and TCP implementation. The key innovative idea is to continuously estimate, at the TCP sender, the packet rate of the connection by monitoring the ACK reception rate. The estimated connection rate is then used to compute congestion window and slow start threshold settings after a congestion episode. Resetting the window to match available bandwidth makes TCPW more robust to sporadic losses due to wireless channel problems. These often cause conventional TCP to overreact, leading to unnecessary window reduction. Experimental studies of TCPW show significant improvements in throughput performance over Reno and SACK, particularly in mixed wired/wireless networks over high-speed links. The contributions of this paper include a model for fair and friendly sharing of the bottleneck link and a Markov Chain performance model in presence of link errors/loss. TCPW performance is compared to that of TCP Reno, and analytic results are validated against simulation results. Internet and laboratory measurements using a Linux TCPW implementation are also reported, providing further evidence of the gains achievable via TCPW.

We present a performance model of TCP Westwood (TCPW), a new TCP protocol with a sender-side modification of the window congestion control scheme. TCP Westwood controls the window using end-to-end connection bandwidth share estimation, obtained by monitoring the ACK reception rate. An analytic model using Markov Chain techniques is developed in this paper, and then used to assess the performance improvements obtained using TCPW. The model takes into account the estimation and filtering method used in TCPW, as well as the following system parameters, bottleneck link bandwidth, buffer space at the bottleneck router, end-to-end propagation time, and error rate. The model reveals substantial TCPW gains over Reno whenever losses due to link or other errors are taken into consideration. The analytic model accuracy is confirmed by comparing to simulation results.

We present our experiences in implementing and validating the on-demand multicast routing protocol (ODMRP) in a real wireless ad hoc network testbed. ODMRP maintains a mesh for each multicast group to provide multiple alternate paths. Redundancy created by the mesh helps overcome frequent topology changes resulting from node mobility, channel fading, and interferences. The protocol does not maintain permanent route tables with full topological views. Instead, multicast senders reactively and dynamically discover routes and obtain multicast group information on demand. ODMRP is implemented in our testbed network consisting of six hosts using the kernel level multicast support option built into the Linux operating system. We describe the key design and implementation features of our protocol and report preliminary testbed experiment results of ODMRP and DVMRP (distance vector multicast routing protocol), a traditional tree based scheme.

Bluetooth is a new low-cost wireless technology that is going to play an important role in communications among small electronic devices and the access to wired networking infrastructure. Bluetooth stations that communicate directly form a piconet. In a piconet one station has the role of master and the others are slaves. The access to the medium is based on a TDD (time division duplexing) scheme controlled by the master. The master sends packets to slaves in even-numbered slots triggering a transmission from slaves in the subsequent slot. Slaves are allowed to send packets only in response to a master packet. The way in which the master schedules packets transmission to slaves or polls them determines system performance. We consider the problem of designing an efficient and simple polling and scheduling scheme for Bluetooth. We propose some practical schemes and compare their performance with some ideal schemes derived from known results for polling systems.

To protect against possible network node or link failure and achieve high reliability of communications, pre-planned failure recovery schemes are needed in modern high-speed communication networks. A couple of schemes have been previously reported for multicast communications. We present a scheme based on a "dual-tree" structure in which a secondary tree for fault-tolerance purpose is built as a complement to a primary multicast tree. The secondary tree provides alternative delivery paths that can be activated when link or node failure is detected in the primary multicast tree. Simulation experiments show that this scheme has shorter restoration time and cause less multicast tree cost increase after restoration than some schemes proposed previously.

The standard end-to-end flow control implemented by the TCP protocol is ill-suited when it comes to achieving fair bandwidth allocation among competing TCP flows. Indeed, the lack of feedback from intermediate nodes does not allow a TCP source to regulate its throughput so that it is not sending more than its fair share, thus penalizing other, less aggressive flows. We propose a novel scheme that, building on existing work on network-layer stateless fair queueing, extends the approach to the TCP layer. Also, we discuss a possible implementation of both the network-layer and the transport-layer architecture. We test our solution under different traffic scenarios and show that not only is a fair bandwidth allocation achieved, but the overall network utilization for TCP flows is also increased.

Higher layer protocols in wireless networks need to dynamically adapt to observed network response. A common approach is for each protocol to employ an end-to-end monitoring and measuring mechanism and estimate quantities of interest, usually related to delay, latency or bandwidth. A less conventional approach is to employ network layer feedback mechanisms in place or in aid of end-to-end efforts. In this paper we use an 802.11-based link throughput and permissible throughput measurement. In our experiments these source-destination pair permissible throughput measurements are propagated in a multi-hop network using the AODV algorithm. In this setting, we are investigating how source rate adaptive multimedia applications can make use of this network feedback. We find that the investigated network feedback approach provides a strong network control feature, an accurate and timely available measurement at the sources, while the overhead of supporting and maintaining it is minimal. Finally, we argue that network based feedback approaches are particularly promising for higher layer protocol support and soft-QoS support in wireless networks.

In recent years, routing has been the most focused area in ad hoc networks research. On-demand routing in particular, is widely developed in bandwidth constrained mobile wireless ad hoc networks because of its effectiveness and efficiency. Most proposed on-demand routing protocols however, build and rely on a single route for each data session. Whenever there is a link disconnection on the active route, the routing protocol must perform a route recovery process. In QoS routing for wired networks, multiple path routing is popularly used. Multiple routes are however, constructed using link-state or distance vector algorithms which are not well-suited for ad hoc networks. We propose an on-demand routing scheme called split multipath routing (SMR) that establishes and utilizes multiple routes of maximally disjoint paths. Providing multiple routes helps minimizing route recovery process and control message overhead. Our protocol uses a per-packet allocation scheme to distribute data packets into multiple paths of active sessions. This traffic distribution efficiently utilizes available network resources and prevents nodes of the route from being congested in heavily loaded traffic situations. We evaluate the performance of our scheme using extensive simulation.

Ad hoc networks are deployed in situations where no base station is available and a network has to be built impromptu. Since there is no wired backbone, each host is a router and a packet forwarder. Each node may be mobile, and topology changes frequently and unpredictably. Routing protocol development has received much attention because mobility management and efficient bandwidth and power usage are critical in ad hoc networks. No existing protocol however, considers the load as the main route selection criteria. This routing philosophy can lead to network congestion and create bottlenecks. We present dynamic load-aware routing (DLAR) protocol that considers intermediate node routing loads as the primary route selection metric. The protocol also monitors the congestion status of active routes and reconstructs the path when nodes of the route have their interface queue overloaded. We describe three DLAR algorithms and show their effectiveness by presenting and comparing simulation results with an ad hoc routing protocol that uses the shortest paths.

Generalized processor sharing (GPS) has gained much popularity as a simple and effective scheduling mechanism for the provisioning of quality of service (QoS) in emerging high-speed networks. For supporting deterministic end-to-end delay guarantees, GPS is known to be sub-optimal in comparison to the earliest deadline first (EDF) scheduling discipline; nevertheless it is often prefered over EDF due to its simplicity. In this paper, using analytical frameworks developed in the literature, we reassess the merits of GPS as compared to EDF in the setting of statistical delay service. Our contributions are threefold. The statistical frameworks in the literature enable the aggregate losses (i.e., delay bound violations) at an EDF scheduler to be estimated-our first contribution, therefore, is to develop a mechanism that allows the aggregate losses to translate to per-flow guarantees. This is achieved by means of a simple packet discard scheme that drops packets fairly then delay violations are imminent at the EDF scheduler. The discard mechanism has a constant complexity and is feasible for implementation in current packet switches. The ability to derive the per-flow guarantees from the aggregate allows a direct comparison between EDF and GPS-our next contribution, therefore, is to show for various traffic mixes with given per-flow loss constraints that EDF offers consistently larger schedulable regions than GPS, both in the single-hop and multi-hop setting. As our final contribution, we argue that the use of GPS for statistical delay support is inherently problematic. We demonstrate that achieving the maximal schedulable regions under GPS could necessitate dynamic resynchronization of the GPS weights, an operation considered infeasible for practical implementation.

TCP Westwood (TCPW) is a sender-side modification of the TCP congestion window algorithm that improves upon the performance of TCP Reno in wired as well as wireless networks. The improvement is most significant in wireless networks with lossy links, since TCP Westwood relies on end-to-end bandwidth estimation to discriminate the cause of packet loss (congestion or wireless channel effect) which is a major problem in TCP Reno. An important distinguishing feature of TCP Westwood with respect to previous wireless TCP “extensions” is that it does not require inspection and/or interception of TCP packets at intermediate (proxy) nodes. Rather, it fully complies with the end-to-end TCP design principle. The key innovative idea is to continuously measure at the TCP source the rate of the connection by monitoring the rate of returning ACKs. The estimate is then used to compute congestion window and slow start threshold after a congestion episode, that is, after three duplicate acknowledgments or after a timeout. The rationale of this strategy is simple: in contrast with TCP Reno, which “blindly” halves the congestion window after three duplicate ACKs, TCP Westwood attempts to select a slow start threshold and a congestion window which are consistent with the effective bandwidth used at the time congestion is experienced. We call this mechanism faster recovery. The proposed mechanism is particularly effective over wireless links where sporadic losses due to radio channel problems are often misinterpreted as a symptom of congestion by current TCP schemes and thus lead to an unnecessary window reduction. Experimental studies reveal improvements in throughput performance, as well as in fairness. In addition, friendliness with TCP Reno was observed in a set of experiments showing that TCP Reno connections are not starved by TCPW connections. Most importantly, TCPW is extremely effective in mixed wired and wireless networks where throughput improvements of up to 550% are observed. Finally, TCPW performs almost as well as localized link layer approaches such as the popular Snoop scheme, without incurring the O/H of a specialized link layer protocol.

We study the bidirectional shufflenet topology, which is obtained from the well-known (unidirectional) shufflenet by considering bidirectional links. More specifically, we define a shortest path routing algorithm, and derive the diameter and the average distance of the topology. The bidirectional shufflenet is then compared, in terms of average distance, with other variations of the perfect shuffle. Bidirectional links are very common in real networks. Possible applications of bidirectional shufflenets are wormhole routing electronic networks with back-pressure flow control, and wavelength routing optical networks. The former class of networks is considered, when virtual channels are used to prevent deadlocks. We show that four virtual channels are sufficient to avoid deadlocks in the bidirectional shufflenet, regardless of the number of nodes in the topology.

QoS-constrained routing is considered as one of the key components to support quality of service in next-generation data networks. However, the optimal routing problem subject to multiple constraints is NP-hard in general. In this paper we propose a technique called "smart forwarding" which can be used in both distributed hop-by-hop QoS routing and centralized source-based routing. It enables fast on-demand routing by utilizing a table pre-computed with link-state information or distributed Bellman-Ford algorithm. It can greatly reduce routing overhead in both flooding-based and crank-back routing protocols by only forwarding routing request to a neighbor that is known to be able or potentially be able to meet the QoS requirement. We also describe how we can adjust routing overhead by bounding the number of flooding or crank-back trials with this technique. More detailed analysis of this technique with delay-constrained routing is presented with simulation results which demonstrate that smart forwarding technique is effective in finding a low-cost path while it has the property of being able to find a feasible solution if there is one.

We present an enhanced version of the routing protocol, Landmark Ad Hoc Routing (LANMAR). LANMAR combines the features of Fisheye State Routing (FSR) and Landmark routing. The enhanced version features landmark election to cope with the dynamic and mobile environment. Other advantages of LANMAR include the use of landmarks for each logical group (e.g., a team of co-workers at a convention or a tank battalion in the battlefield) in order to reduce routing update overhead in large networks, and the exchanging of neighborhood link state only with neighbors. When the network size grows, remote groups of nodes are "summarized" by the corresponding landmarks. As a result, each node will maintain accurate routing information about immediate neighborhood; at the same time it will keep track of the routing directions to the landmark nodes and thus, to remote groups. Simulation experiments show that the enhanced version suffers some performance degradation at steady state because of election overhead. However, it still provides an efficient and scalable routing solution in a mobile, ad hoc environment. Moreover, the election provides a much needed recovery from landmark failures.

This paper proposes a feedback based algorithm for congestion control and bandwidth allocation in the presence of either TCP traffic or both TCP and real time traffic. In this proposal, the network layer conveys bandwidth and propagation delay measurements to data sources, for instance using IPv6 optional fields. TCP sources use this bandwidth delay product to control their congestion window, while video sources use the available bandwidth feedback to adjust their data sending rate. The experiments show that with this approach, the network achieves stable equilibrium, and users, either transmitting TCP traffic or real-time traffic, can share network resources fairly. Furthermore, since TCP sources learn about the available bandwidth independent of packet loss, there is no need to reduce the congestion window following a packet loss. This provides a way to improve the TCP performance in wireless networks where it is difficult to distinguish between congestion loss and radio channel interference loss.

We propose the use of QoS routing to enhance the support of IP telephony. Our proposed scheme is based on QoS intradomain OSPF routing, an extension of the conventional OSPF routing protocol. A DiffServ model is used (no per flow signaling, nor per flow accounting at intermediate nodes). Processing O/H is shifted from core to edge routers, which compute routes, monitor QoS path quality and enforce call acceptance control (CAC) using the link state information advertised by OSPF. Via simulation, we show significant delay and throughput improvement over IP telephony strategies currently used in the Internet. In particular, hot spots and focussed congestion points are easily avoided. Moreover, the ability to control voice via QoS routing and CAC permits us to adjust the capacity sharing between voice traffic and TCP traffic, by reserving a fraction of link bandwidth to TCP data traffic. We also show that the added control and processing overhead is quite manageable, even in fairly large networks.

This paper presents a novel routing protocol for wireless ad hoc networks-fisheye state routing (FSR). FSR introduces the notion of multi-level fisheye scope to reduce routing update overhead in large networks. Nodes exchange link state entries with their neighbors with a frequency which depends on distance to destination. From link state entries, nodes construct the topology map of the entire network and compute optimal routes. Simulation experiments show that FSR is a simple, efficient and scalable routing solution in a mobile, ad hoc environment.

The on-demand multicast routing protocol (ODMRP) is an effective and efficient routing protocol designed for mobile wireless ad hoc networks. One of the major strengths of ODMRP is its capability to operate both as a unicast and a multicast routing protocol. This versatility of ODMRP can increase network efficiency as the network can handle both unicast and multicast traffic with one protocol. We describe the unicast functionality of ODMRP and analyze the protocol performance in a real ad hoc network testbed of seven laptop computers in an indoor environment. Both static and dynamic networks are deployed. We generate various topological scenarios in our wireless testbed by applying mobility to network hosts and study their impacts on our protocol performance. We believe that the performance study in a testbed network can help us analyze the protocol in a realistic way and indicate the direction for future research.

To support QoS for multicast with dynamic and distributed member joining, in this paper we present a receiver-initiated multicast protocol with multiple QoS constraints (RIMQoS). Assuming link-state information and QoS unicast routing protocol are available, a receiver computes a path to join the multicast tree rooted at the source. It then sends join request along the path to join the group. Our protocol specifies under what conditions the new member can be accepted into the group without affecting the QoS of other members and how to adjust the existing tree if necessary. It attempts to minimize the cost of the tree by letting a node join the tree via a low-cost path and may later switch to a higher-cost but more QoS stringent path when necessary. The proposed scheme allows fully distributed operation and supports multiple QoS metrics and requirements. It greatly reduces the number of messages and simplifies message processing to join members compared with some other approaches. Simulation results show that it is very efficient in finding low-cost solutions.

In this paper we investigate the performance of multicast routing protocols in wireless mobile ad hoc networks. An ad hoc network is composed of mobile nodes without the presence of a wired support infrastructure. In this environment, routing/multicasting protocols are faced with the challenge of producing multihop routes under host mobility and bandwidth constraints. In recent years, a number of new multicast protocols of different styles have been proposed for ad hoc networks. However, systematic performance evaluations and comparative analysis of these protocols in a common realistic environment has not yet been performed. In this study, we simulate a set of representative wireless ad hoc multicast protocols and evaluate them in various network scenarios. The relative strengths, weaknesses, and applicability of each multicast protocol to diverse situations are studied and discussed.

In this paper, we present a novel routing protocol for wireless ad hoc networks-landmark ad hoc routing (LANMAR). LANMAR combines the features of fisheye state routing (FSR) and landmark routing. The key novelty is the use of landmarks for each set of nodes which move as a group (e.g., a team of co-workers at a convention or a tank battalion in the battlefield) in order to reduce routing update overhead. Like in FSR, nodes exchange link state only with their neighbors. Routes within the fisheye scope are accurate, while routes to remote groups of nodes are "summarized" by the corresponding landmarks. A packet directed to a remote destination initially aims at the landmark; as a gets closer to the destination it eventually switches to the accurate route provided by fisheye. Simulation experiments show that LANMAR provides efficient and scalable routing in large, mobile, ad hoc environments in which group mobility applies.

This paper presents on-demand routing scalability improvements achieved using a "passive" clustering. Any on-demand routing typically requires some form of flooding. Clustering can dramatically reduce transmission overhead during flooding. In fact, by using clustering, we restrict the set of forwarding nodes during flood search and thus reduce the energy cost and traffic overhead of routing in dynamic traffic and topology environments. However existing "active" clustering mechanisms require periodic refresh of neighborhood information and tend to introduce quite a large amount of communication maintenance overhead. We introduce a passive clustering protocol scheme which is mostly supported/maintained by user data packets instead of explicit control packets. The passive scheme is consistent with the on-demand routing philosophy. Simulation results show significant performance improvements when passive clustering is used.

Multi-layer ad hoc wireless networks with UAVs is an ideal infrastructure to establish a rapidly deployable wireless communication system any time any where in the world for military applications. In this tactical environment, information traffic is quite asymmetric. Ground fighting units are information consumers and receive far more data than they transmit. The up-link is used for sending requests for information and some networking configuration overhead with a few kilobits, while the down-link is used to return the data requested with megabits size (e.g. multimedia file of images and charts). Centralized intelligent channel assigned multiple access (C-ICAMA) is a MAC layer protocol proposed for ground backbone nodes to access UAV (unmanned aerial vehicle) to solve the highly asymmetric data traffic in this tactical environment. With it's intelligent scheduling algorithm, it can dynamically allocate bandwidth for up-link and downlink to fit the instantaneous status of asymmetric traffic. The results of C-ICAMA is very promising, due to the dynamic bandwidth allocation of asymmetric up-link and down-link, the access delay is tremendously reduced.

Large homogeneous ad hoc wireless networks have a problem: the bandwidth available to a mobile user decreases as the number of nodes in the network increases. Using the embedded ad-hoc networking mechanism, nodes are able to transport packets across the network in a multihop fashion. An embedded mobile backbone is dynamically constructed to form a 2-level physical heterogeneous multihop wireless network. These backbone nodes provide two critical functions: (1) direct communication between neighboring cluster heads; and (2) efficient route discovery in HSR. With the broadcast feature of unmanned aerial vehicle (UAV), the link state can be broadcast to backbone nodes instead of "flooding" on the level 2. Thus, the routing overhead can be tremendously reduced, and the throughput will be improved. We modified hierarchical state routing (HSR) to have an intelligent selection algorithm to reduce the system latency caused by the long propagation delay of the UAV channel. The performance of the system is evaluated through simulation experiments.

Nodes in mobile ad hoc networks communicate with one another via packet radios on wireless multihop links. Because of node mobility and power limitations, the network topology changes frequently. Routing protocols therefore play an important role in mobile multihop network communications. A trend in ad hoc network routing is the reactive on-demand philosophy where routes are established only when required. Most of the protocols in this category, however, use a single route and do not utilize multiple alternate paths. We propose a scheme to improve existing on-demand routing protocols by creating a mesh and providing multiple alternate routes. Our algorithm establishes the mesh and multipaths without transmitting any extra control message. We apply our scheme to the Ad-hoc On-Demand Distance Vector (AODV) protocol and evaluate the performance improvements by simulation.

An ad hoc wireless network is composed of mobile hosts without any wired infrastructure support. In mobile ad hoc networks, unicast and multicast routing protocols are faced with the challenge of producing multihop routes because of limited radio propagation range. In addition, routing protocols must manage mobility and be bandwidth and power efficient. The on-demand multicast routing protocol (ODMRP) is a protocol designed for ad hoc networks with multicast purposes. Two unique features of ODMRP are its unicast capability and its utilization of a mobility prediction scheme to perform rerouting in anticipation of route disconnection. We describe ODMRP unicast routing functionality and assess the mobility prediction effectiveness and efficiency. We evaluate the ODMRP performance via detailed simulation and compare it with other ad hoc routing schemes.

Wireless communications are becoming an important part of our everyday lifestyle. One major area that will have an enormous impact on the performance of wireless ad hoc networks is the medium access control (MAC) layer. Current random access MAC protocols for ad hoc networks support reliable unicast but not reliable broadcast. We propose a random access MAC protocol, broadcast support multiple access (BSMA), which improves the broadcast reliability in ad hoc networks.

Ad-hoc wireless networks cannot easily support multimedia applications because of the media high probability, burstiness and persistence of errors. Real-time constraints and multicast make the problem even more difficult. Therefore, in order to improve their performance over the existing best-effort networks, multimedia applications must adapt their operation to constantly changing network QoS. In this paper we propose a programming model that allows audio applications to adapt to changes in network QoS. In our scheme QoS information is continuously fed back from audio clients to the audio server, which uses this information to adapt the characteristics of an audio stream to fit the current network conditions. We have implemented an audio-on-demand application for the Windows NT platform that uses this model. We present experiments that confirm the usefulness of our adaptation mechanism for improving the packet loss and delay jitter characteristics of an audio channel in networks with unpredictable QoS behavior. In introducing an ultimate speech layer, we incorporate techniques such as captioning, speech recognition and speech synthesizing. When the QoS notification indicates, this minimal layer takes over to maintain an acceptable level of meaningful communication. Our experiments, both in a simulated and in a real multihop wireless testbed, show that our QoS mechanism improves the characteristics of the audio channel. End user perception can be greatly enhanced, and meaningful communication can be sustained even at most adverse network conditions by using our speech transcription scheme.

In this study we investigate the interaction between TCP and MAC layer in a wireless multi-hop network. This type of network has traditionally found applications in the military (automated battlefield), law enforcement (search and rescue) and disaster recovery (flood, earthquake), where there is no fixed wired infrastructure. Wireless "ad-hoc" multi-hop networks have previously been proposed for nomadic computing applications. Key requirements in all the above applications are reliable data transfer and congestion control, features that are generally supported by TCP. Unfortunately, TCP performs on wireless in a much less predictable way than on wired protocols. Using simulation, we provide new insight into two critical problems of TCP over wireless multi-hop. The first is the conflict between data packets and ACKs, which causes TCP performance to degrade for window sizes greater than 1 packet. The second is the interaction between MAC and TCP layer backoff timers which causes severe unfairness and capture conditions. In the paper, we identify these problems in several representative simulation runs on various topologies and traffic patterns and indicate possible remedies to improve TCP efficiency over a wireless multi-hop network.

In the presence of satellite channels, one of the most challenging problems for TCP is to achieve fair bandwidth sharing among several competing connections with round-trip propagation delays that may differ by more than two orders of magnitude. The bandwidth-aware TCP (BA-TCP) provides a fair solution while maintaining the end-to-end semantics of transport protocols. At the same time, it allows backward compatibility and it does not require substantial changes to the existing TCP. In BA-TCP, the network layer is assumed to be able to convey propagation delay and available bandwidth measurements to end users, for instance using IPv6 optional fields. TCP receivers employ this information to compute a generalized advertised window, which, in turn, controls the amount of data the source injects into the network. Experimental results show that a satellite connection can fairly share a bottleneck with wired connections. Furthermore, since BA-TCP exploits the bandwidth-delay product to control the source congestion window, the queuing delay at the bottleneck link tends to zero at steady state and buffer overflow is negligible in most situations.

An ad hoc wireless network is an infrastructureless network composed of mobile hosts. The primary concerns in ad hoc networks are bandwidth limitations and unpredictable topology changes. Thus, efficient utilization of routing packets and immediate recovery of route breaks are critical in routing and multicasting protocols. A multicast scheme, on-demand multicast routing protocol (ODMRP), has been recently proposed for mobile ad hoc networks. ODMRP is a reactive (on-demand) protocol that delivers packets to destinations on a mesh topology using scoped flooding of data. A number of enhancements can be applied to improve the performance of ODMRP. In this paper, we propose a mobility prediction scheme to help select stable routes and to perform rerouting in anticipation of topology changes. We also introduce techniques to improve transmission reliability and eliminate route acquisition latency. The impact of our improvements is evaluated via simulation.

In this paper, we consider the mobility management in large, hierarchically organized multihop wireless networks. The examples of such networks range from battlefield networks, to emergency disaster relief and law enforcement etc. We present a novel network addressing architecture to accommodate mobility using a "home agent" concept akin to mobile IP. The performance of the mobility management scheme is investigated through simulations.

Mobile computing will be much used in the future, as is evident by such initiatives as Bluetooth, Iceberg and HomeRF. However, for mobile computing to be successful, an obvious layer, the MAC layer, must be efficient in channel access and reservation. Therefore, in-depth understanding is needed of the wireless MAC layer if wireless computing is to takeoff. Many random access wireless MAC protocols have been proposed and standardized. However, there has not yet been an attempt to understand why certain designs are used and what makes certain protocols better than others. In this paper, we survey several popular, contemporary, wireless, random access MAC protocols and determine the effects behind the design choices on these protocols.

Congestion control of Internet best effort traffic relies mostly on TCP window flow control of individual sessions. This paper argues that such approach does not scale well to a very large number of simultaneously active flows, typical of backbones characterized by large delay-bandwidth products. In this scenario, the TCP window sizes tend to be small and dropping or marking packets alone is not effective to reduce the offered traffic. The analysis presented describes the aggressive TCP dynamics under many flows and suggests that the performance can be improved by applying back-pressure flow control to the aggregate traffic in the backbone. To demonstrated this argument, a link-layer, rate-based, back-pressure mechanism for IP-over-ATM backbones using the ABR service is described. A simulation study of a network with this capability demonstrates the improvement of TCP performance under many flows. The study also considers RED and ECN routers to indicate that these techniques alone are not well positioned to address the many flows scenario either. However, the combination of random early detection (RED) and explicit congestion notification (ECN) routers with back-pressure has the potential to further improve TCP performance.

Fairness in the Internet is becoming a major obstacle for the introduction of commercial services. In this paper we address the problem of fairness with a slightly non-standard approach: we show that, in order to achieve fairness in the Internet, it is enough to provide good congestion control, without the need for explicit computation of fairness indexes. We first introduce a TCP-based congestion scheme that takes into account available bandwidth resources on links, describing how this scheme can be easily introduced as a TCP option in end-systems; it requires neither a centralized approach in routers, nor a per-flow management of traffic. Then several scenarios are analyzed via simulation, showing how and to what degree fairness is achieved. Results are compared with a traditional TCP-Reno implementation with RED routers. Finally, the coexistence of the new TCP version with traditional implementations is discussed.

This paper presents a novel multicast routing protocol for mobile ad hoc wireless networks. The protocol, termed ODMRP (on-demand multicast routing protocol), is a mesh-based, rather than a conventional tree-based multicast scheme and uses a forwarding group concept (only a subset of nodes forwards the multicast packets via scoped flooding). It applies on-demand procedures to dynamically build routes and maintain multicast group membership. ODMRP is well suited for ad hoc wireless networks with mobile hosts where bandwidth is limited, topology changes frequently, and power is constrained. We evaluate ODMRP's scalability and performance via simulation.

In this paper we present a hierarchical routing protocol in a large wireless, mobile network such as found in the automated battlefield or in extensive disaster recovery operations. Conventional routing does not scale well to network size. Likewise, conventional hierarchical routing cannot handle mobility efficiently. We propose a novel soft state wireless hierarchical routing protocol-Hierarchical State Routing (HSR). We distinguish between the "physical" routing hierarchy (dictated by geographical relationships between nodes) and "logical" hierarchy of subnets in which the members move as a group (e.g., company, brigade, battalion in the battlefield). HSR keeps track of logical subnet movements using home agent concepts akin to Mobile IP. A group mobility model is introduced and the performance of the HSR is evaluated through a detailed wireless simulation model.

We consider a large population of mobile stations that are interconnected by a multihop wireless network. The applications of this wireless infrastructure range from ad hoc networking (e.g., collaborative, distributed computing) to disaster recovery (e.g., fire, flood, earthquake), law enforcement (e.g., crowd control, search-and-rescue), and military (automated battlefield). Key characteristics of this system are the large number of users, their mobility, and the need to operate without the support of a fixed (wired or wireless) infrastructure. The last feature sets this system apart from existing cellular systems and in fact makes its design much more challenging. In this environment, we investigate routing strategies that scale well to large populations and can handle mobility. In addition, we address the need to support multimedia communications, with low latency requirements for interactive traffic and quality-of-service (QoS) support for real-time streams (voice/video). In the wireless routing area, several schemes have already been proposed and implemented (e.g., hierarchical routing, on-demand routing, etc.). We introduce two new schemes-fisheye state routing (FSR) and hierarchical state routing (HSR)-which offer some competitive advantages over the existing schemes. We compare the performance of existing and proposed schemes via simulation.

In an ad-hoc environment with no wired communication infrastructure, it is necessary that mobile hosts operate as routers in order to maintain the information about connectivity. However with the presence of high mobility and low signal/interference ratio (SIR), traditional routing schemes for wired networks are not appropriate, as they either lack the ability to quickly reflect the changing topology, or may cause excessive overhead, which degrades network performance. Considering these restrictions, we propose a new scheme especially designed for routing in an ad-hoc wireless environments. We call this scheme "global state routing" (GSR), where nodes exchange vectors of link states among their neighbors during routing information exchange. Based on the link state vectors, nodes maintain a global knowledge of the network topology and optimize their routing decisions locally. The performance of the algorithm, studied in this paper through a series of simulations, reveals that this scheme provides a better solution than existing approaches in a truly mobile, ad-hoc environment.

New services have been defined to allow the Internet to address the demands of new multimedia applications. Meeting the quality of service requirements for these services involves implementing new features on routers and bandwidth management is a key aspect of this effort. In this paper we compare the use of the ABR versus the CBR service to provide bandwidth and real-time commitments to the multimedia traffic on Internet backbones over ATM. We discuss effective throughput and delay trade-offs for a traffic mix using best effort (BE) and non-BE services. We also extend the class based queueing features to trigger bandwidth re-negotiations.

In this paper we address the evaluation of speech quality through a wireless network as perceived by the user. User perceived evaluation (in addition to the usual network metrics including delay, throughput, packet loss statistics, etc.) is critical in the design of wireless multimedia networks where speech and video play a key role and are affected by several factors, such as network performance and encoding scheme. We use two approaches for our evaluation: small scale testbed implementation and hybrid simulation. The testbeds are implemented either by UDP (user datagram protocol) connection or UCLA talk connection. The hybrid simulation is event driven and is based on the Maisie parallel simulation language. It uses speech traces for inputs and plays back the speech outputs off-line. There are several advantages in using the simulation tool, mainly from the point of view of scalability and new protocol feature testing. At the same time, the real life testbed provides verification of the simulator assumptions, albeit on a small scale.

We propose an "on-demand" multicast routing protocol for a wireless, mobile, multihop network. The proposed scheme has two key features: (a) it is based on the forwarding group concept (i.e., a subset of nodes is in charge of forwarding the multicast packets via scoped flooding) rather than on the conventional multicast tree scheme (b) it dynamically refreshes the forward group members using a procedure akin to on-demand routing (hence the name). "On-demand" multicast is well suited to operate in an on-demand routing environment where routes are selectively computed as needed between communicating node pairs instead of being maintained and updated globally by a routing "infrastructure" (like in distance vector or link state, for example). On-demand multicast is particularly attractive in mobile, rapidly changing networks, where the traffic overhead caused by routing updates and tree reconfigurations may become prohibitive beyond a critical speed; and in large network with sparse traffic requirements, where the traffic, processing and storage overhead of the routing infrastructure solution compromises scalability. Via simulation, we compare on-demand multicast with a traditional tree multicast scheme, DVMRP, and with a version of forwarding group multicast which uses conventional distance vector routing instead of on-demand routing. This allows us to assess the penalty of the tree and of the global routing infrastructure as a function of mobility and sparseness.

In this paper we study the bidirectional shufflenet topology, which is obtained from the well-known (unidirectional) shufflenet by considering bidirectional links. More specifically, we define a shortest-path routing algorithm, and derive the diameter and the average distance of the topology. The bidirectional shufflenet is then compared, in terms of average distance, with other variations of the perfect shuffle.

In this paper we propose a multicast protocol for a multihop, mobile wireless network with cluster based routing and token access protocol within each cluster. The multicast protocol uses a shared tree which is dynamically updated to adjust to changes in topology and membership (i.e. dynamic joins and quits). Two options for tree maintenance have been simulated and evaluated: "hard state" (i.e. each connection must be explicitly cleared) and "soft state" (each connection is automatically timed out and must be refreshed). For the soft state policy, the performance of different choices of timeout and refresh timers is first analyzed for a range of node mobility values. Next, soft state and hard state policies are compared based on throughput, join delay, and control overhead criteria.

LAN multicast is now an essential service for users of the MBone and other IP multicast tools. Traditional IP multicast has travelled over two types of subnetwork: point-to-point links and subnetworks with inherent multicast capability, such as Ethernet and token ring. More recent LANs may be arbitrary mesh networks with no built-in, efficient, multicast capability. The authors describe a successful implementation of multicasting over a 640 Mbit/s, wormhole-routing LAN. The implementation is integrated with the wider-area multicast IP service. Consideration is given to practical issues such as interoperation with existing multicast routing protocols and software, and multicast-group setup latencies.

Personal communications and mobile computing will require a wireless network infrastructure which is fast deployable, possibly multihop, and capable of multimedia service support. The first infracture of this type was the packet radio network (PRNET), developed in the 70's to address the battlefield and disaster recovery communication requirements. PRNET was totally asynchronous and was based on a completely distributed architecture. It handled datagram traffic reasonably well, but did not offer efficient multimedia support. Recently, under the WAMIS and Glomo ARPA programs several mobile, multimedia, multihop (M/sup 3/) wireless network architectures have been developed, which assume some form of synchronous, time division infrastructure. The synchronous time frame leads to efficient multimedia support implementations. However, it introduces more complexity and is less robust in the face of mobility and channel fading. In this paper; we examine the impact of synchronization on wireless M/sup 3/ network performance. First, we introduce MACA/PR, an asynchronous network based on the collision avoidance MAC scheme employed in the IEEE 802.11 standard. There, we evaluate and compare several wireless packet networks ranging from the total asynchronous PRNET to the synchronized cluster TDMA network. We examine the tradeoffs between time synchronization and performance in various traffic and mobility environments.

In order to minimize latency in high-speed interconnection networks, the wormhole routing technique can be employed. With this technique, a switch transmits an incoming message as soon as it receives it, without waiting for the entire message. The problem then is that a message stretches over several links and locks network resources, thus making a contention situation possible. Two principal congestion control mechanisms cast be considered, backpressure flow control and deflection routing. The performance of these mechanisms depends both on the traffic characteristics and on the network topology. In order to compare them, we study analytically the behavior of a wormhole routing network model with random input traffic under both policies. We estimate the probability of collision between messages and express the average message transit delay as a function of the offered load. Simulation provides a good confirmation for the analytical results. This study gives us an understanding of the behavior of the system under different resource management policies.

A novel wireless MAC protocol named MACA-BI (MACA By Invitation) is introduced. MACA-BI is a simplified version of the well known MACA (Multiple Access Collision Avoidance) protocol, which is based on the request to send/clear to send (RTS/CTS) handshake and which has inspired the IEEE 802.11 wireless LAN standard. In MACA-BI, the RTS part of the RTS/CTS handshake is suppressed, leaving only the clear to send a control message which can be viewed as an "invitation" by the receiver to transmit. This reduction greatly improves the efficiency when radio turn-around time is significant with respect to packet transmission time. Yet, it preserves the "data" collision free property of MACA. Simulation results for various multihop topologies show that, when the traffic characteristics are stationary or predictable, MACA-BI outperforms several known multiple access protocols, especially when "hidden terminal" conditions are predominant.

This paper describes a self-organizing, multihop, mobile radio network which relies on a code-division access scheme for multimedia support. In the proposed network architecture, nodes are organized into nonoverlapping clusters. The clusters are independently controlled, and are dynamically reconfigured as the nodes move. This network architecture has three main advantages. First, it provides spatial reuse of the bandwidth due to node clustering. Second, bandwidth can be shared or reserved in a controlled fashion in each cluster. Finally, the cluster algorithm is robust in the face of topological changes caused by node motion, node failure, and node insertion/removal. Simulation shows that this architecture provides an efficient, stable infrastructure for the integration of different types of traffic in a dynamic radio network.

Wormhole routing networks have become increasingly popular for low latency, high-speed interconnection of supercomputer and workstation clusters. An example is the Supercomputer SuperNet (SSN) at UCLA, which interconnects supercomputers across campus and metropolitan area distances. The SSN employs a two-level network architecture in which an optical backbone network interconnects several high-speed, wormhole-routing local area networks (Myrinets). The SSN applications such as scientific visualization and rendering require that the network support reliable delivery of traffic characterized by quality of service (QoS) parameters. Motivated by this requirement, we investigate QoS support in Myrinet-like high-speed, wormhole routing networks. Since native Myrinet protocols do not provide QoS support, we explore several novel strategies including (a) the use of a separate subnet for carrying such traffic (along with source pacing), (b) the overlay of a virtual synchronous system on the asynchronous network, and (c) the introduction of virtual channels. We discuss the tradeoffs among the different options and evaluate them via selected simulation experiments.

The Supercomputer SuperNet (SSN) is a two-level hierarchical high-speed network. The lower level is a high speed electronic mesh fabric; the higher level is a WDM optical backbone network interconnecting the high-speed fabrics distributed across a campus or metropolitan area. The salient characteristics of this architecture are the use of wormhole routing and backpressure hop-by-hop flow control mechanism. Because of these features, deadlocks are possible in SSN. In this paper, we address the issue of deadlock-free routing which is an essential prerequisite for the proper operation of SSN. To this end, we first present a deadlock free routing scheme for the WDM backbone which is implemented with a shufflenet multihop virtual topology. We use the notion of virtual channels to obtain mappings of virtual channels to physical channels such that deadlock-free routing is achieved for any (p,k) shufflenet (uni and bidirectional). Then, we compare the virtual channels scheme with the more conventional up/down deadlock free routing scheme for the bidirectional shufflenet and show that the former yields much better performance. Finally, we address the problem of deadlock prevention across the entire network (i.e., lower level fabric as well as the optical backbone) and develop an integrated solution combining different schemes best suited for the different levels.

Presents a feedback control algorithm for ATM congestion control in which source rates are adjusted according to VC queue lengths at intermediate nodes along the path. The goal is to "fill in" the residual bandwidth, without exceeding a specified queue threshold. In order to obtain this, we propose a simple and classical proportional controller, plus a Smith predictor to overcome instabilities due to large propagation delays, as well as to avoid cell loss. We propose an effective EPRCA implementation in which each source computes its input rate based on the maximum VC queue length along the path. Theoretical and experimental results show that high throughput is achieved even with queue sizes independent of the round trip delay.

Wormhole routing LANs are emerging as an effective solution for high-bandwidth, low-latency interconnects in distributed computing and cluster computing applications. An important example is the 640 Mb/s crossbar-based Myrinet. A key property of conventional LANs, which is valuable for many distributed applications, is transparent, reliable network-level multicast. It is desirable to retain this property also in wormhole LANs. Unfortunately, efficient, reliable multicasting in wormhole LANs is problematic because of the potential for deadlocks. As a consequence, current multicasting implementations typically consist of repeated unicast or assume a priori buffer reservations. These solutions, however, tend to increase latency and do not scale well.In this paper we address the problem of providing transparent, reliable, efficient network level multicasting in the wormhole LAN. We describe several protocols for achieving deadlock-free, reliable multicasting using restricted routing and fast buffer reservation techniques. Tradeoffs involving complexity and performance of various solutions are discussed, and are illustrated using simulation. A simple multicast implementation for Myrinet has been carried out, and experimental results are presented.

The traditional shufflenet multihop virtual topology for optical networks does not provide easy support for backpressure flow control on a hop-by-hop basis. In the context of an optical backbone network interconnecting high speed electronic LANs that use wormhole routing, as in the Supercomputer SuperNet (SSN) project, hop-by-hop flow control is required in the optical network to eliminate losses due to buffer overflows. We modify the shufflenet topology by using bidirectional links to obtain a new topology called bidirectional shufflenet. This topology provides a natural support for the hop-by-hop backpressure flow control mechanism. We demonstrate the need for flow control in the wormhole routing context. We compare the average hops with the shufflenet and bilayered shufflenet. Then, we compare shufflenet with bidirectional shufflenet via simulation to show the performance improvements yielded by the latter. The throughput of the bidirectional shufflenet is better for large worms while the delay is comparable. The length of the worm has a clear effect on the throughput and delay values obtained.

The paper presents a distributed architecture which relies on code division access scheme for multimedia transport in a wireless mobile radio network without a fixed infrastructure. The proposed multicluster architecture has the capability of rapid deployment and dynamic reconfiguration. Without the need of base stations, this architecture can operate in areas without a wired back-bone infrastructure. The presented architecture has two main advantages. First, this architecture can provide spatial reuse of the bandwidth due to node clustering. Second, computer simulation reveals that our cluster structure is robust in the face of topological changes due to node motion, node failure, and/or new node addition. In all, this architecture provides a stable infrastructure for the integration of different types of traffic in a dynamic radio network.

Optical networks can provide higher throughputs while high speed electronic networks possess the intelligence for network control and management. We present a two level high speed network architecture that combines the throughput advantage of optical networks and the intelligence of electronic processing. One level is a high speed mesh LAN which uses wormhole routing, source routing and hop-by-hop flow control mechanisms with mesh routers (asynchronous pipelined crossbar switches) to provide a high speed electronic network. The second level is an optical star network interconnecting high speed mesh networks distributed across metropolitan area distances. We obtain analytical expressions for the average message (worm) delays for the GTDM (group time division multiplexing) multi-access protocol (which includes as special cases TDM and DAS) for single-hop packet switching in the optical network of such an architecture. We use a two state discrete time Markov chain to model the arrival of messages to the optical network. Results for both uniform traffic and non-uniform traffic are presented. Finally, a modified dynamic allocation scheme is presented for single-hop packet switching which handles the message as a unit rather than sending a message as several fixed sized packets.