This work presents an attack to undermine MAC address randomization using a dual-layer approach combining PHY and MAC-layer analysis. By passively collecting CSI features along with MAC-layer behavioral patterns, our system applies an XGBoost classifier to distinguish devices enabling MAC randomization in dense networks, achieving up to 100% precision and 86% recall.

We present results for exposing vulnerabilities in MAC address randomization using Wi-Fi network discovery traffic collected at MobiCom 2023. By analyzing probe request sequence numbers and vendor-specific information elements, we successfully link randomized MAC addresses, reducing the observed MAC addresses to linked groups by over 45%. This demonstrates current MAC randomization protocols inadequately protect device privacy during network discovery.

To prevent tracking a Wi-Fi device based on its MAC address, several operating systems have adopted MAC address randomization to conceal its factory-assigned address. This feature benefits users when their devices scan for networks, but a flaw arises when timing between transmissions stays consistent despite MAC address randomization in use. We present a defense mechanism, implemented with the Netlink library, against a time correlation attack for probe request packets on Wi-Fi devices. We show how adding random jitter to probe request transmissions renders a timing correlation attack infeasible to track devices during network discovery.

This paper presents Lamina, a system for providing security and privacy to users in a public IoT space. Public IoT spaces, such as an IoT-enable retail store, have the potential to provide rich, targeted information and services to users within the environment. However, to fully realize such potential, users must be willing to share certain data regarding their habits and preferences with the public IoT spaces. To encourage users to share such information, we present Lamina, a system that ensures the user's data will not be leaked to third parties. Lamina uses CryptoCoP-based encryption and a unique MAC address rotation mechanism to ensure that a user's privacy is maintained and their data is protected while still allowing the public IoT space to collect sufficient information to effectively provide targeted services.

The increased contention and collisions in dense networks trigger excessive scans for finding AP. The collective effect of simultaneous probes from all devices create even more contention in the network. Eventually, the devices start continuous cycles of probing since network condition does not improve after the handoff. Traces we have collected during Infocom 2012 and at busy airport terminals show this impact of probing on dense networks. In this paper, we propose Dynamo-Probing that obtains AP information from nearby active scan using its novel scan mode, Opp-Scan, and by switching to active scan when such opportunities are not available. By avoiding sending probes for each device in the network, Dynamo-Probing reduces the network overload due to probing and thus improves communication quality. Results from our ns-2 simulations capture a 78% improvements in network association time and up to an 82% improvements in throughput for very dense networks. By being adaptive to network density and interoperable with legacy devices, Dynamo-Probing provides an appropriate scan solution that ensures survival in dense networks and good performance in sparse networks.

Provides a brief professional biography of the presenter. The presentation (including an abstract) was not made available for publication as part of the conference proceedings.

SaveAlert is an adaptive framework for crowd-monitoring and danger-detection using off-the-shelf smartphones and other peripherals such as smartwatches. It is a system that provides users with an increased awareness of their surroundings by detecting and notifying them of impending danger, by relying only on sensor data collected from the users. Our framework's novelty is in how it performs efficient sensor data collection from potentially a large number of people by limiting the disturbance and stress on the existing Wi-Fi and cellular infrastructure. To the best of our knowledge, this is the first crowd-monitoring framework that takes advantage of peer-to-peer connections to perform local aggregation to alleviate the stress on existing infrastructures for better scalability and efficiency.

SaveAlert is an adaptive framework for danger-detection using existing devices such as off-the-shelf smartphones and smartwatches. The framework can be extended to different sensors that could trigger distress signals to notify nearby users of potentially dangerous situations.

This paper presents a novel multicopy routing protocol for disruption-tolerant networks whose objective is to minimize energy expended on communication. The protocol is designed for disaster-response applications, where power and infrastructure resources are disrupted. Unlike other delay-tolerant networks, energy is a vital resource in post disaster scenarios to ensure availability of (disruption-tolerant) communication until infrastructure is restored. Our approach exploits naturally recurrent mobility and contact patterns in the network, formed by rescue workers, volunteers, survivors, and their (possibly stranded) vehicles to reduce the number of message copies needed to attain an adequate delivery ratio in the face of disconnection and intermittent connectivity. A new notion of intercontact routing is proposed that allows estimating route delays and delivery probabilities, identifying more reliable routes and controlling message replication and forwarding accordingly. In addition, we augment the protocol with a differentiated message delivery service that enables the network to function even in an extremely low energy condition. We simulate the scheme using a mobility model that reflects recurrence inspired by disaster scenarios and compare our results to previous DTN routing techniques. The evaluation shows that the new approach reduces the resource overhead per message over previous approaches while maintaining a comparable delivery ratio at the expense of a small (bounded) increase in latency.

One of the key features of high speed WLAN such as 802.11n is the use of MIMO (Multiple Input Multiple Output) antenna technology. The MIMO channel is described with fine granularity by Channel State Information (CSI) that can be utilized in many ways to improve network performance. Many complex parameters of a MIMO system require numerous samples to obtain CSI for all possible channel configurations. As a result, measuring the complete CSI space requires excessive sampling overhead and thus degrades network performance. We propose CSI-SF (CSI Sampling & Fusion), a method for estimating CSI for every MIMO configuration by sampling a small number of frames transmitted with different settings and extrapolating data for the remaining settings. For instance, we predict CSI of multi-stream settings using CSI obtained only from single stream packets. We evaluate the effectiveness of CSI-SF in various scenarios using our 802.11n testbed and show that CSI-SF provides an accurate, complete knowledge of the MIMO channel with reduced overhead from traditional sampling. We also show that CSI-SF can be applied to network algorithms such as rate adaptation, antenna selection and association control to significantly improve their performance and efficiency.

The high vulnerability of the wireless sensor nodes to jamming arises from the low resilience and easy differentiability of protocol control messages, and the high predictability of node wakeup schedules. In this paper, we propose Jam-Buster - a jam-resistant solution for WSN, orthogonal to the existing antijamming solutions, that increases resilience by using multi-block payloads, eliminates differentiation by using equal size packets and reduces predictability by randomizing the wakeup times of the sensors. While each of these individual components is quite simple, the combination of the three components results in a jam-resilient system that forces the jammer to transmit more enabling faster detection of the jammer by the sensors, and to spend more energy to be effective and so reduce its own lifetime. By modeling our system using game theory and then evaluating the system in a TmoteSky testbed, we show that Jam-Buster reduces the overall efficiency of an intelligent jammer.

The rapid deployment of millions of mobile sensors and smartphones has resulted in a demand for opportunistic encounter-based networking to support mobile social networking applications and proximity-based gaming. However, the success of these emerging networks is limited by the lack of effective and energy efficient neighbor discovery protocols. While probabilistic approaches perform well for the average case, they exhibit long tails resulting in high upper bounds on neighbor discovery time. Recent deterministic protocols, which allow nodes to wake up at specific timeslots according to a particular pattern, improve on the worst case bound, but do so by sacrificing average case performance. In response to these limitations, we have designed Searchlight, a highly effective asynchronous discovery protocol that is built on three basic ideas. First, it leverages the constant offset between periodic awake slots to design a simple probing-based approach to ensure discovery. Second, it allows awake slots to cover larger sections of time, which ultimately reduces total awake time drastically. Finally, Searchlight has the option to employ probabilistic techniques with its deterministic approach that can considerably improve its performance in the average case when all nodes have the same duty cycle. We validate Searchlight through analysis and real-world experiments on smartphones that show considerable improvement (up to 50%) in worst-case discovery latency over existing approaches in almost all cases, irrespective of duty cycle symmetry.

poster Share on LoadingZones: leveraging street parking to enable vehicular internet access Authors: Riccardo Crepaldi University of Illinois, Urbana-Champaign, IL, USA University of Illinois, Urbana-Champaign, IL, USAView Profile , Ryan Beavers University of Illinois, Urbana-Champaign, IL, USA University of Illinois, Urbana-Champaign, IL, USAView Profile , Braden Ehrat University of Illinois, Urbana-Champaign, IL, USA University of Illinois, Urbana-Champaign, IL, USAView Profile , Jason Sze University of Illinois, Urbana-Champaign, IL, USA University of Illinois, Urbana-Champaign, IL, USAView Profile , Matt Jaeger University of Illinois, Urbana-Champaign, IL, USA University of Illinois, Urbana-Champaign, IL, USAView Profile , Steven Biersteker University of Illinois, Urbana-Champaign, IL, USA University of Illinois, Urbana-Champaign, IL, USAView Profile , Robin Kravets University of Illinois, Urbana-Champaign, IL, USA University of Illinois, Urbana-Champaign, IL, USAView Profile Authors Info & Claims Mobicom '12: Proceedings of the 18th annual international conference on Mobile computing and networkingAugust 2012Pages 415–418https://doi.org/10.1145/2348543.2348598Published:22 August 2012Publication History 1citation235DownloadsMetricsTotal Citations1Total Downloads235Last 12 Months0Last 6 weeks0 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Publisher SiteGet Access

No abstract available.

No abstract available.

No abstract available.

The high vulnerability of nodes in a WSN to jamming arises from the low resilience to jamming signals, easy differentiability of packet types and high predictability of wakeup schedules. In this paper, we propose Jam-Buster - a jam-resistant solution for a single channel WSN that increases resilience by using multi-block payload, eliminates differentiation by using equal size packets and reduces predictability by randomizing the wakeup times of the sensors. While each of these individual components is quite simple, the combination of the three components results in a jam-resilient system that forces the jammer to spend more energy to be effective and so reduce its own lifetime.

Delay in a duty-cycled network occurs when the sender waits for its receiver to be awake. Exploiting multiple receivers instead of a single receiver at each hop allows the sender to use the node that wakes up the soonest and so reduce delay. However, current MAC-layer anycast protocols either suffer from high signaling or synchronization overhead and are only appropriate for low duty cycle, low traffic scenarios. In this paper, we propose Any-MAC - a generic, low overhead extension that can be applied to any existing asynchronous MAC protocol to enable MAC-layer anycast. The extensive research in duty-cycle protocols provides us many MAC protocols, each appropriate for a particular network and application scenario. Thus, to construct an anycast solution to reduce delay for a specific network scenario, Any-MAC simply needs to extend the appropriate MAC protocol designed for that scenario. By applying anycast to existing protocols, X-MAC and NPM, we show that Any-MAC uses only simple modification to the base protocols and improves the performance significantly. Our evaluations in ns-2 show that with Any-MAC, both protocols can achieve 30% improvements in delay by exploiting the inherent route level redundancy in the network.

The widespread availability of mobile wireless devices offers growing opportunities for the formation of temporary networks with only intermittent connectivity. These intermittently-connected networks (ICNs) typically lack stable end-to-end paths. In order to improve the delivery rates of the networks, new store-carry-and-forward protocols have been proposed which often use message replication as a forwarding mechanism. Message replication is effective at improving delivery, but given the limited resources of ICN nodes, such as buffer space, bandwidth and energy, as well as the highly dynamic nature of these networks, replication can easily overwhelm node resources. In this work we propose a novel node-based replication management algorithm which addresses buffer congestion by dynamically limiting the replication a node performs during each encounter. The insight for our algorithm comes from a stochastic model of message delivery in ICNs with constrained buffer space. We show through simulation that our algorithm is effective, nearly tripling delivery rates in some scenarios, and imposes little overhead.

Wireless sensor networks typically conserve energy by following a periodic wakeup-sleep schedule: nodes minimize idle time and spend most of their time in a low power sleep state. In order to communicate and exchange data in such a network, the current duty-cycling MAC protocols either require tight synchronization between the neighbor wakeup schedules or spend a significant amount of energy in signaling the sleeping nodes. In contrast, this paper presents Neighborhood-based Power Management (NPM), an energy efficient asynchronous MAC protocol that minimizes signaling overhead through opportunistically gained knowledge about neighbor wakeup schedules. Unlike the synchronization-based MAC protocols, NPM does not require a priori knowledge of the wakeup schedules. Using only a minimal exchange of schedule information, NPM reduces the signaling overhead by shortening the wakeup signal. Furthermore, NPM uses its wakeup signal to awaken all receivers in the neighborhood of the sender, enabling all sender-receiver pairs in that neighborhood to communicate. Our extensive evaluations show that NPM outperforms popular B-MAC, X-MAC and SCP protocols under all network conditions. NPM reduces the signaling overhead, with up to 74% savings in energy and 80% reduction in delay.

This paper presents Pirrus, a replica management system that addresses the problem of providing data availability on a wireless sensor network. Pirrus uses probabilistic failure models (e.g., derived from environmental conditions and estimation of available energy) to adaptively create and maintain a number of replicas of the data. Replica management is formulated as an energy optimization problem, then solved with a greedy heuristic that only uses information gathered from neighbors. Intuitively, Pirrus trades off the energy saved by limiting the number of replicas when the network health is good to extend the lifetime when more replicas are needed. Our simulation results show how the solution provided by Pirrus achieves good performance with a sustainable computational cost. Compared to the performance of a fixed number of replicas, Pirrus extends the network lifetime by more than 20%.

Current work in routing protocols for delay and disruption tolerant networks leverage epidemic-style algorithms that trade off injecting many copies of messages into the network for increased probability of message delivery. However, such techniques can cause a large amount of contention in the network, increase overall delays, and drain each mobile node's limited battery supply. We present a new DTN routing algorithm, called Encounter-Based Routing (EBR), which maximizes delivery ratios while minimizing overhead and delay. Furthermore, we present a means of securing EBR against black hole denial- of-service attacks. EBR achieves up to a 40% improvement in message delivery over the current state-of-the-art, as well as achieving up to a 145% increase in goodput. Also, we further show how EBR outperforms other protocols by introduce three new composite metrics that better characterize DTN routing performance.

This paper presents a novel multi-copy routing protocol for disruption-tolerant networks whose objective is to minimize energy expended on communication. The protocol is designed for disaster-response applications, where power and infrastructure resources are disrupted. Unlike other delay-tolerant networks, energy is a vital resource in post-disaster scenarios to ensure availability of (disruption-tolerant) communication until infrastructure is restored. Our approach exploits naturally recurrent mobility and contact patterns in the network, formed by rescue workers, volunteers, survivors, and their (possibly stranded) vehicles to reduce the number of message copies needed to attain an adequate delivery ratio in the face of disconnection and intermittent connectivity. A new notion of inter-contact routing is proposed that allows estimating route delays and delivery probabilities, identifying more reliable routes and controlling message replication and forwarding accordingly. We simulate the scheme using a mobility model that reflects recurrence inspired by disaster scenarios, and compare our results to previous DTN routing techniques. The evaluation shows that the new approach reduces the resource overhead per message over previous approaches while maintaining a comparable delivery ratio at the expense of a small (bounded) increase in latency.

Low power radios, such as the CC2420, have been widely popular with recent sensor platforms. This paper explores the potential for energy savings from adding a high-power, high-bandwidth radio to current sensor platforms. High-bandwidth radios consume more power but significantly reduce the time for transmissions. Consequently, they offer net savings in total communication energy when there is enough data to offset wake-up energy overhead. The analysis on energy characteristics of several IEEE 802.11 radios show that a feasible crossover point exists (in terms of data size) after which energy savings are possible. Based on this analysis, we present a bulk data transmission protocol for dual radio systems. The results of simulations and prototype implementation show significant energy savings at the expense of introducing acceptable delay.

As mobile systems become increasing prevalent, they are being called upon to run multimedia applications traditionally associated with the wired domain. Unfortunately, battery capacity is not keeping pace with system demand, driving the demand for energy efficiency. Unfortunately, the encapsulation of traditional layered designs limits the energy that can be saved because layers cannot cooperate. However, monolithic systems have been shown to be inefficient and unscalable. In this paper, we present the design and implementation of a system consisting of multiple adaptive applications, and adaptive MAC and transport layers. We evaluate this system by implementing an adaptive video encoding application, showing that a layered approach sharing enough information can enable energy efficiency while maintaining sufficient isolation to allow the replacement of components without requiring a whole-system redesign.

A large majority of the Internet traffic relies on TCP as its transport protocol. In future, as the edge of the Internet continues to extend over the wireless medium, TCP (or its close variants) may not prove to be appropriate. The key reason is in TCP’s inability to discriminate congestion losses from transmission losses. Since transmission losses are frequent in wireless networks, the penalty from loss misclassification can become high, leading to performance degradation. This paper presents an eXtended Rate-based Transport Protocol (XRTP), designed to support communication over lossy wireless media. We depart from the ack-based rate control paradigm. Instead, we try to estimate the network conditions by injecting probe packets at the sender, and then observing the spacing between packets that arrive at the receiver. We show that these observations can be useful indicators of available bandwidth, network congestion, and even the cause of packet loss. The inferences from the observations are utilized to regulate the transmission rate at the sender, leading to desirable properties of congestion control and loss discrimination. Simulation results show the efficacy of our proposed rate-based protocol in lossy wireless environments.

Multimedia applications have unique characteristics that can be leveraged to design energy-efficient loss recovery mechanisms. Given their loss tolerance and strict timing requirements, various frame dropping policies can be used to affect both application performance and energy consumption. However, the effects on energy consumption of such frame dropping policies depends on not only high-layer effects, but also the MAC layer underlying them. Therefore, we first present an analysis of an energy-efficient MAC-layer protocol, called Fast Transmit MAC Protocol (FTMP). We then explore three frame dropping policies: proactive, reactive, and opportunistic. We present the EELR (energy-efficient loss recovery) protocol, which uniquely combines all three frame dropping policies to provide both high energy efficiency and high application performance. EELR is implemented in a real system on top of an energy-saving MAC layer that exposes information about transmission costs to the transport layer for use in frame dropping decisions. Through analysis and real-world experiments, we show that the combination of an energy-efficient MAC layer with a transport protocol using all three frame-drop policies outperforms any other combination.

Power-management approaches have been widely studied in an attempt to conserve idling energy by allowing nodes to switch to a low-power sleep mode. However, due to the inherent inability of current approaches to match sleep schedules to different traffic patterns, energy is wasted switching needlessly from sleep to idle or large delays in traffic delivery are incurred due to being in the sleep state too long. In this paper, we explore such effects of various traffic patterns on current power management protocols. Our results show the importance of traffic information to obtain larger benefits from power management. While some proposals that exploit traffic information exist, they rely primarily on individual sender traffic patterns to develop sleep schedules, ignoring aggregate traffic observed by receivers. This deficiency motivates the design of a new power management protocol that use traffic information at the receivers to adapt sleep schedules.

Energy management remains a critical problem in wireless networks since battery technology cannot keep up with rising communication expectations. Current approaches to energy conservation reduce the energy consumption of the wireless interface either for a given communication task or during idling. However, a complete solution requires minimizing the energy spent for both communication (i.e., for data and control overhead) and idling. This problem can be expressed as an energy-efficient network design problem, which is, not surprisingly, NP-hard. Therefore, in this paper, we study three heuristic approaches. Our study shows that the first approach that prioritizes communication energy conservation does not save energy. The second approach, which tries to reduce energy used for both data and in idling, becomes cost-prohibitive due to its high control overhead. Hence, we propose a third approach that prioritizes idling energy conservation. Due to its low control overhead, this approach meets the challenge of operating the network with low energy cost.

Providing efficient and reliable communication in wireless sensor networks is a challenging problem. To recover from corrupted packets, previous approaches have tried to use retransmissions and FEC mechanisms. The energy efficiency of these mechanisms, however, is very sensitive to unreliable links. In this paper, we present cluster-based forwarding, where each node forms a cluster such that any node in the next-hop's cluster can take forwarding responsibility. This architecture, designed specifically for wireless sensor networks, achieves better energy-efficiency by reducing retransmissions. Cluster-based forwarding is not a routing protocol. Rather, it is designed as an extension layer that can augment existing routing protocols. Using simulations, we demonstrate that cluster-based forwarding is effective in improving both end-to-end energy efficiency and latency of current routing protocols.

One key issue in wireless sensor networks is energy efficiency. Aggregation techniques attempt to minimize the energy expended in communication by processing the data in the network rather than forwarding it all to a central point for processing. However, the naive application of this technique can result in a net increase in total energy expenditure due to the computational costs of the processing. In this paper, we present a new model for aggregation in wireless sensor networks, incorporating both the amount of data reduction achieved by the aggregation function and its associated computation costs. We then use this model to create a powerful, lightweight, distributed aggregation tree creation protocol, called Tethys, suitable for implementation in wireless sensor networks. We show that our protocol provides significantly lower energy consumption than protocols which do not take the amount of data reduction and computational cost of aggregation into consideration.

Mobile devices primarily processing multimedia data need to support multimedia quality with limited battery energy. To address this challenging problem, researchers have introduced adaptation into multiple system layers, ranging from hardware to applications. Given these adaptive layers, a new challenge is how to coordinate them to fully exploit the adaptation benefits. This paper presents a novel cross-layer adaptation framework, called GRACE-1, that coordinates the adaptation of the CPU hardware, OS scheduling, and multimedia quality based on users' preferences. To balance the benefits and overhead of cross-layer adaptation, GRACE-1 takes a hierarchical approach: It globally adapts all three layers to large system changes, such as application entry or exit, and internally adapts individual layers to small changes in the processed multimedia data. We have implemented GRACE-1 on an HIP laptop with the adaptive Athlon CPU, Linux-based OS, and video codecs. Our experimental results show that, compared to schemes that adapt only some layers or adapt only to large changes, GRACE-1 reduces the laptop's energy consumption up to 31.4 percent while providing better or the same video quality.

This paper presents a theoretical study on distributed contention window control algorithms for achieving arbitrary bandwidth allocation policies and efficient channel utilization. By modeling different bandwidth allocation policies as an optimal contention window assignment problem, we design a general and fully distributed contention window control algorithm, called GCA (general contention window adaptation), and prove that it converges to the solution of the contention window assignment problem. By examining the stability of GCA, we identify the optimal stable point that maximizes channel utilization and provide solutions to control the stable point of GCA near the optimal point. Due to the generality of GCA, our work provides a theoretical foundation to analyze existing and design new contention window control algorithms.

To reduce idle-time energy consumption, nodes in ad hoc networks can switch to a power-save mode. However, since operating all nodes in power-save mode limits network capacity, some nodes may need to stay in active mode to support forwarding. The main challenge of selecting nodes to stay in active mode stems from the need to conserve energy while maintaining communication. Although topology management protocols build a forwarding backbone of active nodes by powering down redundant nodes, such protocols incur proactive backbone maintenance overhead. The reactive approach, on-demand power management, manages node transitions from active to power-save mode based on routing information. However, node transitions are only traffic-driven and may result in keeping redundant nodes awake. To this end, we propose TITAN, which builds a backbone reactively using information about both ongoing communication and the current power-management mode of nodes. The design of TITAN is based on the trade-offs between waking up power-saving nodes on shorter routes and using longer routes that contain active nodes. Simulation results show that TITAN conserves energy while maintaining efficient communication without additional control overhead for topology management

An admission control algorithm must coordinate between flows to provide guarantees about how the medium is shared. In wired networks, nodes can monitor the medium to see how much bandwidth is being used. However, in ad hoc networks, communication from one node may consume the bandwidth of neighboring nodes. Therefore, the bandwidth consumption of flows and the available resources to a node are not local concepts, but related to the neighboring nodes in carrier-sensing range. Current solutions do not address how to perform admission control in such an environment so that the admitted flows in the network do not exceed network capacity. In this paper, we present a scalable and efficient admission control framework - contention-aware admission control protocol (CACP) - to support QoS in ad hoc networks. We present several options for the design of CACP and compare the performance of these options using both mathematical analysis and simulation results. We also demonstrate the effectiveness of CACP compared to existing approaches through extensive simulations.

We present MPARC (multi-priority admission and rate control), a novel joint admission control and rate policing protocol for multi-priority ad hoc networks. MPARC is based on our novel bandwidth allocation model and guarantees that the throughput of admitted realtime flows will not decrease due to later arriving realtime flows with equal or lower priorities or due to best effort flows. MPARC achieves this goal by performing accurate admission control on every newly arriving realtime flow and appropriate rate policing on all best effort traffic. Through simulation, we demonstrate that MPARC has better performance than existing approaches.

We present composite key management, a novel paradigm for key management in ad hoc networks. While most existing approaches try to fit techniques developed for wired environments into ad hoc networks, our approach works within the specific limitations of ad hoc networks to increase security and availability of the key management framework. By composing techniques from PKI and certificate chaining, composite key management follows two fundamental principles that must be satisfied by an ad hoc key management framework: node participation and the use of a trusted third party. We introduce enhanced metrics of authentication to aid end users in understanding and using the key management framework. Through simulation studies, we demonstrate the effectiveness of composite key management under stressful scenarios where previous approaches fail and show that composite key management can address the challenges posed by the unique nature of ad hoc networks.

In this paper, we propose a new cross-layer framework, named QPART (QoS protocol for ad hoc realtime traffic), which provides QoS guarantees to real-time multimedia applications for wireless ad hoc networks. By adapting the contention window sizes at the MAC layer, QPART schedules packets of flows according to their unique QoS requirements. QPART implements priority-based admission control and conflict resolution to ensure that the requirements of admitted real time flows is smaller than the network capacity. The novelty of QPART is that it is robust to mobility and variances in channel capacity and imposes no control message overhead on the network.

Battery power is an important resource in ad hoc networks. It has been observed that in ad hoc networks, energy consumption does not reflect the communication activities in the network. Many existing energy conservation protocols based on electing a routing backbone for global connectivity are oblivious to traffic characteristics. In this paper, we propose an extensible on-demand power management framework for ad hoc networks that adapts to traffic load. Nodes maintain soft-state timers that determine power management transitions. By monitoring routing control messages and data transmission, these timers are set and refreshed on-demand. Nodes that are not involved in data delivery may go to sleep as supported by the MAC protocol. This soft state is aggregated across multiple flows and its maintenance requires no additional out-of-band messages. We implement a prototype of our framework in the ns-2 simulator that uses the IEEE 802.11 MAC protocol. Simulation studies using our scheme with the dynamic source routing protocol show a reduction in energy consumption near 50% when compared to a network without power management under both long-lived CBR traffic and on-off traffic loads, with comparable throughput and latency. Preliminary results also show that it outperforms existing routing backbone election approaches.

The characteristics of ad hoc networks naturally encourage the deployment of distributed services. Although current networks implement group communication methods, they do not support the needs of a mobile node that must locate one or more distributed servers. A node should not need detailed knowledge of network topology to choose servers with which it can communicate efficiently.To this end, manycast is a group communication scheme that enables communication with an arbitrary (user specified) number of group members. Anycast and multicast communication are special cases of manycast in which the target number of group members is one and infinity, respectively. We present manycast and discuss its use as a communication primitive, with specific attention to ad hoc networks. We advocate manycast support at the network layer. A manycast routing protocol enables an application to contact several nearby network nodes that implement a distributed service.We analyze some approaches to manycast, including some application layer implementations. This evaluation supports our claim that manycast must be implemented in the network layer for effective operation in ad hoc networks. We present several extensions to ad hoc routing protocols that can provide manycast support with minimal implementation effort. Through analysis and extensive simulation, we explore the behavior of these approaches to manycast, finally providing recommendations to implementors.

MobileIP, the standard for Internet mobility, enables transparent mobility for a mobile node, but requires communication to take a multihop path through the node's Home Agent. Although a user with a multiple-interface mobile node may desire the ability to communicate locally, perhaps while disconnected from the Internet, MobileIP offers no such support.Contact Networking provides lightweight, localized network communication to a node with diverse network interfaces. The goal is to provide support for local connectivity equivalent to that provided by MobileIP for remote connectivity. The concept of link-layer awareness enables Contact Networking to tailor its operation to different links, using link-layer native services to implement abstract services when possible. Interface management and autoconfiguration insulate the user from concerns about the number and type of interfaces available.In this paper, we motivate the need for localized mobility, and present the design and architecture of Contact Networking. Details of our prototype implementation illustrate the complexities of providing a localized mobility facility.

ARP handles neighbor discovery and address resolution in infrastructure networks, but is inadequate for mobile ad hoc networks (MANETs). Thus, many MANET routing protocols include a neighbor discovery mechanism. This separation of neighbor discovery and address resolution is a fundamental design problem that causes packet loss, particularly when the communication is manycast, a novel variant of multicast communication. Our approach, automatic address resolution, moves address resolution into the routing protocol along with neighbor discovery, correcting these problems.

Mobile ad hoc networks are autonomous, infrastructureless networks that support multihop communication through IP routing. This paper examines the use of mobile IP in order to provide global Internet connectivity to ad hoc networks that use an on-demand routing protocol. We present a hybrid scheme that uses techniques such as TTL scoping of agent advertisements, eavesdropping and caching agent and advertisements to combine the advantages of proactive and reactive approaches to providing connectivity. We present simulation results to show that our approach achieves excellent connectivity while keeping overhead costs low.

TCP responds to all losses by invoking congestion control and avoidance algorithms, resulting in degraded end-to-end performance in lossy environments. In recent years, two approaches have been taken to improve the performance of TCP in such networks. One is local retransmission and the other is end-to-end control. These schemes either impose a heavy computational burden on base station, or cannot achieve both efficient bandwidth usage and fairness between flows because they cannot distinguish the flows on low quality wireless links from flows on high quality links. In this paper, we present a new wireless TCP protocol-End-to-end Link State Aware TCP (TCP-ELSA)-that adjusts the sending rate of a TCP flow according to the wireless link quality, but still provides good congestion control when congestion-related losses occur. The aim of TCP-ELSA is to adapt the sending rate of TCP to the link quality so that the efficiency of bandwidth usage is increased. We present simulation results that demonstrate the effectiveness of TCP-ELSA in various scenarios.

Since its birth more than two decades ago, public key cryptography has been recognized as one of the most effective mechanisms for providing fundamental security services including authentication, digital signatures and encryption for dynamic networks. Effective management of keys, or digital certificates holding the keys, is one of the key factors for the successful wide-spread deployment of public key cryptography. The public key infrastructure (PKI ), an infrastructure for managing digital certificates, was introduced for this purpose. The most important component of PKI is the certificate authority (CA), the trusted entity in the system that vouches for the validity of digital certificates. This work describes a framework to provide efficient yet effective distributed CA service for ad hoc wireless networks. We select physically or computationally more secure nodes as MOCAs (MObile Certificate Authority) and use threshold cryptography to distribute the CA's private key among these MOCA nodes. We also provide a protocol for clients to contact MOCAs and get certification services without incurring excessive overhead.

ABSTRACT In recent years there have been significant advances in 3D scan-ning technologies that allow the creation of meshes with hundreds of millions of polygons. A number of algorithms have been pro-posed for the display of such large models. These advances, coupled with the steady growth in the speed of network links, havegiven rise to a new area of interest, the streaming transmission and visualization of three-dimensional data sets. We present a numberof issues that must be addressed when designing a transport protocol for three-dimensional images as well as a method of transport.We then evaluate an implementation of an On-Demand Graphic Transport Protocol (OGP) that addresses these issues. Categories and Subject Descriptors C.2.2 [Computer]: Communication Networks

Present mobile computing does not support the simultaneous use of multiple heterogeneous network interfaces for a single transport layer connection. We describe a solution for channel aggregation at the transport layer, which provides increased bandwidth to mobile nodes. We present R-MTP (reliable multiplexing transport protocol), a rate-based reliable transport protocol capable of multiplexing data from a single application data stream across multiple network interfaces. Due to the lossy nature of wireless links in mobile environments, R-MTP tracks packet interarrival time for discrimination between congestion-based and transmission-based losses as well as better bandwidth estimation. The challenges to such a reliable protocol lie in the coordination of packets across streams with varying channel characteristics. Our experimental results validate R-MTP's bandwidth estimation and loss characterization techniques. Successful bandwidth aggregation is demonstrated in ideal and lossy environments.

In mobile computing, power is a limited resource. Like other devices, communication devices need to be properly managed to conserve energy. In this paper, we present the design and implementation of an innovative transport level protocol capable of significantly reduc- ing the power usage of the communication device. The protocol achieves power savings by selectively choosing short periods of time to suspend communications and shut down the communication device. It manages the important task of queuing data for future delivery during periods of communication suspension, and decides when to restart communication. We also address the tradeoff between reducing power consumption and reducing delay for incoming data.