Online games have been played mainly in desktop computers over wired networks because of high speed and intensive computation requirements. The advances in mobile devices and ever increasing wireless link bandwidth motivate us to study whether players can enjoy online gaming over broadband wireless networks such as mobile Worldwide Inter-operability for Microwave Access WiMAX. In this paper, we carry out comprehensive measurements of the World of Warcraft WoW over the mobile WiMAX in Seoul, Korea, and analyze the network performance focusing on two aspects: 1 network layer dynamics such as round trip time, jitter, and packet loss and 2 WiMAX link layer statistics such as the radio signal strength, handovers, and piggyback mechanism. From the empirical data, we set up performance models and evaluate the performance of WoW over WiMAX. We also discuss how to improve the service quality of online gaming over WiMAX.Copyright © 2013 John Wiley & Sons, Ltd.

Named Data Networking (NDN) uses content names as routing entries, and thus the scalability of NDN routing is of primary concern. NDN allows in-network caching as a built-in functionality; however, if network nodes make caching decisions individually, duplicate copies of the same content may exist among nearby nodes. To address these problems, we propose Coordinated Routing and Caching (CoRC) that mitigates routing scalability and enhances the efficiency of the in-network storage. CoRC aligns the routing and caching mechanisms to manage the same content namespace for better performance. We evaluate CoRC (and its variants) with Vanilla NDN in terms of the cache hit ratio, hop count, and traffic load by running software routers on Amazon EC2. To demonstrate the feasibility of CoRC, we also implement and test the processing time of CoRC forwarding in Linux machines.

While the current Internet has a host-based TCP/IP architecture, the vast majority of Internet usage is attributed to the content retrieval and distribution. This mismatch has proliferated content delivery network (CDN) technologies and P2P file-sharing systems (e.g., BitTorrent); however, the inefficiency of content delivery is not fundamentally solved, and there are business/operation and content copyright/availability issues, respectively. Also, in the research community, there have been efforts to redesign the current architecture from a content-centric perspective by introducing the route-by-name paradigm and in-network caching, which however entails many issues like the routing scalability and processing overhead. We propose a lookup-based communication framework for content-oriented networking (LOCON), whose main components are locator lookup, coordinated caching, and parallel transmissions. LOCON aims to accommodate incremental deployment, support legacy end-hosts, and provide business incentives between network operators and content publishers. To carry out the experiments, we build a networking testbed on top of Amazon data centers around the world. LOCON performs better than other lookup-by-name networking technologies and CCN (i.e., a route-by-name scheme) in terms of content delivery metrics.

Pinterest, a popular social curating service where people collect, organize, and share content (pins in Pinterest), has gained great attention in recent years. Despite the increasing interest in Pinterest, little research has paid attention to how people collect, manage, and share pins in Pinterest. In this paper, to shed insight on such issues, we study the following questions. How do people collect and manage pins by their tastes in Pinterest? What factors do mainly drive people to share their pins in Pinterest? How do the characteristics of users (e.g., gender, popularity, country) or properties of pins (e.g., category, topic) play roles in propagating pins in Pinterest? To answer these questions, we have conducted a measurement study on patterns of pin curating and sharing in Pinterest. By keeping track of all the newly posted and shared pins in each category (e.g., animal, kids, women's fashion) from June 5 to July 18, 2013, we built 350 K pin propagation trees for 3 M users. With the dataset, we investigate: (1) how users collect and curate pins, (2) how users share their pins and why, and (3) how users are related by shared pins of interest. Our key finding is that pin propagation in Pinterest is mostly driven by pin's properties like its topic, not by user's characteristics like her number of followers. We further show that users in the same community in the interest graph (i.e., representing the relations among users) of Pinterest share pins (i) in the same category with 94% probability and (ii) of the same URL where pins come from with 89% probability. Finally, we explore the implications of our findings for predicting how pins are shared in Pinterest.

Understanding the group characteristics in MMORPGs is important in user behavior studies since people tend to gather together and form groups due to their inherent nature. In this paper, we analyze the group activities of users in Aion, one of the largest MMORPGs, based on the records of the activities of 94,497 users. In particular, we focus on (i) how social interactions within a group differ from the ones across groups, (ii) what makes a group rise, sustain, or fall, (iii) how group members join and leave a group, and (iv) what makes a group end. We first find that structural patterns of social interactions within a group are more likely to be close-knit and reciprocative than the ones across groups. We also observe that members in a rising group (i.e., the number of members increases) are more cohesive, and communicate with more evenly within the group than the ones in other groups. Our analysis further reveals that if a group is not cohesive, not actively communicating, or not evenly communicating among members, members of the group tend to leave.

While accurate and complete modeling of the Internet topology at the Autonomous System (AS) level is critical for future protocol design, performance evaluation, simulation and analysis, still it remains a challenge to construct its accurate representation. In this paper, we collect BGP route announcements of ASes from Looking glass (LG) servers. By querying LG servers, we build an AS topology estimate of around 116 K AS links, from which we discover 11 K new AS links and 686 new ASes. We conclude that collecting BGP traces from LG servers can help enhance the current view of the AS topology from the BGP collector projects (e.g., RouteViews).

Video on demand services have been increasingly proliferated in the Internet. One popular way to disseminate video files among numerous users is to leverage peer-to-peer (P2P) systems (e.g., BitTorrent). However, BitTorrent is not designed with video streaming requirements and hence suffers from long setup delay. In this paper, the drawbacks of existing P2P-based streaming solutions are analyzed in terms of sequential delivery. Then we propose Waterfall that splits the whole swarm into multiple swarms, which are then cascaded by the scene sequence. In this way, peers in a swarm download the chunks of the same video scene from the peers in the same swarm as well as the ones in the preceding swarm that already moved on to the next scene. The average setup delay and maximum playback rate of Waterfall are analyzed. Experiments from a wide area network testbed reveal that Waterfall achieves two to three times higher playback rate and significantly low setup delay than the prior BitTorrent-based streaming solutions.

The problem of developing distributed scheduling algorithms for high throughput in multihop wireless networks has been extensively studied in recent years. The design of a distributed low-complexity scheduling algorithm becomes even more challenging when taking into account a physical interference model, which requires the SINR at a receiver to be checked when making scheduling decisions. To do so, we need to check whether a transmission failure is caused by interference due to simultaneous transmissions from distant nodes. In this paper, we propose a scheduling algorithm under a physical interference model, which is amenable to distributed implementation with 802.11 CSMA technologies. The proposed scheduling algorithm is shown to achieve throughput optimality. We present two variations of the algorithm to enhance the delay performance and to reduce the control overhead, respectively, while retaining throughput optimality.

The The ever increasing traffic demand is a serious concern of mobile network operators, and the conventional pull-based (or request-based) communication model may not be able to handle this data explosion problem. To reduce the traffic load on cellular links for disseminating content, we propose to push the content to a subset of subscribers via cellular links, and to allow the subscribers to share the content via opportunistic local connectivity (i.e. Wi-Fi ad-hoc mode). We theoretically model and analyze how the content can be disseminated by both pushing via cellular links and sharing via Wi-Fi links, where handovers are modeled based on the multi-compartment model. We also formulate a mathematical framework to optimize the content dissemination, by which the trade-off between the dissemination delay and the energy cost is explored.

We conduct comprehensive measurements on the current practice of content bundling to understand the structural patterns of torrents and the participant behaviors of swarms on one of the largest BitTorrent portals: The Pirate Bay. From the datasets of the 120K torrents and 14.8M peers, we investigate what constitutes torrents and how users participate in swarms from the perspective of bundling, across different content categories: Movie, TV, Porn, Music, Application, Game and E-book. In particular, we focus on: (1) how prevalent content bundling is, (2) how and what files are bundled into torrents, (3) what motivates publishers to bundle files, and (4) how peers access the bundled files. We find that over 72% of BitTorrent torrents contain multiple files, which indicates that bundling is widely used for file sharing. We reveal that profit-driven BitTorrent publishers who promote their own web sites for financial gains like advertising tend to prefer to use the bundling. We also observe that most files (94%) in a bundle torrent are selected by users and the bundle torrents are more popular than the single (or non-bundle) ones on average. Overall, there are notable differences in the structural patterns of torrents and swarm characteristics (i) across different content categories and (ii) between single and bundle torrents.

ABSTRACT In wireless network convergence, each mobile host is expected to have multiple kinds of wireless interfaces. Multicast‐based applications are expected to be widely deployed. In this paper, a new network selection scheme is proposed for a mobile host to select the most appropriate wireless access network to maximize user satisfaction and ISP's profit, simultaneously. We have devised a metric to measure a user's satisfaction and we also developed a ‘normalized network resource’ metric for system profit measure. We have compared our scheme with three other reference schemes, through simulations. Depending on the network deployment situations, our scheme exhibits one‐fifth service disruption time of other reference schemes, while the resource consumption of our scheme is comparable to that of the minimum resource scheme. Overall, the gain of our scheme becomes higher as users move faster and/or the population density increases. Copyright © 2010 John Wiley & Sons, Ltd.

BitTorrent has achieved a great success in the field of peer-to-peer (P2P) file sharing. Although BitTorrent allows peers to share files efficiently and scalably, it shows inefficiency when a client participates in multiple torrents where each of them concurrently competing for the limited link bandwidth. In this paper, we propose a new bandwidth allocation algorithm, which greedily increases the bandwidth consumption for downloading, to reduce file transfer time considering the current download/upload status. To compensate overall performance degradation resulting from our greedy allocation, we suggest modifying the choking algorithm of BitTorrent to consider the ratio of seeders and leechers in each torrent. Through comprehensive experiments, we validate the performance gain of the proposed scheme over original BitTorrent in a mix of WiFi and Ethernet testbed and large scale public torrents.

Since Internet routers are not aware of the contents being forwarded, the same content file is often delivered multiple times inefficiently. Similarly, users cannot exploit a nearby copy of the content of interest unless the content file is serviced by costly content delivery networks. Prior studies on the content-aware routing for efficient content delivery suffer from the scalability problem due to a large number of contents. We propose a scalable content routing, dubbed SCAN, which can exploit nearby and multiple content copies for the efficient delivery. SCAN exchanges the information of the cached contents using Bloom filter. Compared with IP routing, SCAN can offer reduced delivery latency, reduced traffic volume, and load balancing among links.

Surveillance systems are developed to enhance security and safety by constantly observing locations of interest. Although those systems can observe scenes from each camera separately, it is difficult to keep track of any moving target across different cameras. This paper firstly proposes Video Diary Service (VDS) to solve this problem. VDS is an automatic diary service, which makes it possible to keep track of users' lives. In addition, VDS can identify social networking relationships among the users while each camera is watching multiple users. By exploiting these properties of VDS, we extend VDS into a new surveillance system called S-VDS. We also illustrate a few application scenarios where the proposed system can enhance security and safety.

Despite the increasing interest in content bundling in BitTorrent systems, there are still few empirical studies on the bundling practice in real BitTorrent communities. In this paper, we conduct comprehensive measurements on one of the largest BitTorrent portals: The Pirate Bay. From the torrents data set collected for 38 days from April to May, 2010, we study how prevalent bundling is and how many files are bundled in a torrent, across different types of contents shared: Movie, Porn, TV, Music, Application, E-book, and Game.

With the advent of various multimedia streaming applications requiring reliability and high bandwidth, multicasting in wireless LANs has been gaining more attentions as the supported bit rate increases. However, according to the specification of the IEEE 802.11 standard, broadcast/multicast frames are transmitted at a fixed and low bit rate due to the absence of a feedback mechanism such as ACK. This simple broadcasting technique with no feedback signal raises some issues; reliability, efficiency and fairness. In this paper, hence, we propose a framework for multicasting termed Leader-Based Multicast Service (LBMS) to alleviate those limitations. LBMS consists of a leader-based transmission and feedback mechanism for multicasting by extending the IEEE 802.11v standard, which is the next-generation standard for network management. Also, we try to support legacy 802.11 stations can still participate in multicasting. Simulation exhibits that the gain of the proposed multicasting scheme increases as (i) more stations compete for the channel, and (ii) the wireless channel condition becomes poorer.

This paper proposes a service differentiation architecture using virtualization of mobile femtocell. Network-prefix division multiple access (NDMA) is proposed to enable mobile devices inside a moving space to access the Internet with different service demands. With the NDMA scheme, our architecture provides multiple virtual mobile networks for diverse services which are optimized under different network conditions. We experimented on the operation of the proposed architecture with testbed implementation. The result shows the ability of multiple degrees of QoS over each virtual mobile network with additional benefits of personalization, mobility management aggregation, and so on.

Recent research on Internet traffic classification has yield a number of data mining techniques for distinguishing types of traffic, but no systematic analysis on "Why" some algorithms achieve high accuracies. In pursuit of empirically grounded answers to the "Why" question, which is critical in understanding and establishing a scientific ground for traffic classification research, this paper reveals the three sources of the discriminative power in classifying the Internet application traffic: (i) ports, (ii) the sizes of the first one-two (for UDP flows) or four-five (for TCP flows) packets, and (iii) discretization of those features. We find that C4.5 performs the best under any circumstances, as well as the reason why; because the algorithm discretizes input features during classification operations. We also find that the entropy-based Minimum Description Length discretization on ports and packet size features substantially improve the classification accuracy of every machine learning algorithm tested (by as much as 59.8%!) and make all of them achieve >93% accuracy on average without any algorithm-specific tuning processes. Our results indicate that dealing with the ports and packet size features as discrete nominal intervals, not as continuous numbers, is the essential basis for accurate traffic classification (i.e., the features should be discretized first), regardless of classification algorithms to use.

The problem of developing high-performance distributed scheduling algorithms for multi-hop wireless networks has seen enormous interest in recent years. The problem is especially challenging when studied under a physical interference model, which requires the SINR at the receiver to be above a certain threshold for decoding success. Under such an SINR model, transmission failure may be caused by interference due to simultaneous transmissions from far away nodes, which exacerbates the difficulty in developing a distributed algorithm. In this paper, we propose a scheduling algorithm that exploits carrier sensing and show that the algorithm is not only amenable to distributed implementation, but also results in throughput optimality. Our algorithm has a feature called the dual-state approach, which separates the transmission schedules from the system state and can be shown to improve delay performance.

As mobile Internet environments are becoming dominant, how to revamp P2P operations for mobile hosts is gaining more and more attention. In this paper, we carry out empirical traffic measurement of BitTorrent service in various settings (static, bus and subway) in commercial WiMAX networks. To this end, we analyze the connectivity among peers, the download throughput/stability, and the signaling overhead of mobile WiMAX hosts in comparison to a wired (Ethernet) host. We find out the drawbacks of BitTorrent operations in mobile Internet are characterized by lower connection ratio, unstable connections amongst peers, and higher control message overhead.

Flooding, that is to deliver a packet from one node to all other nodes in the network, is an integral part of many wireless protocols. Flooding is often implemented by a series of broadcasts of each node and this causes some problems such as the broadcast storm and low reliability, by being engaged with the effects of radio signal propagation, e.g., multipath fading and interference. Many researchers have studied these problems over the years, however, most of these studies have been carried out assuming that all nodes in the network are equipped with a single radio interface and utilize only a single channel. This implies that most of the existing mechanisms that enhance the performance of flooding in wireless networks will not work in multi-radio multi-channel wireless mesh networks (MR-MC WMNs). Motivated by this, in this paper, we propose a flooding mechanism that works well in MR-MC WMNs. Our flooding mechanism, which can operate with an arbitrary number of radio interfaces and channels, increases the reliability of flooding while alleviates the broadcast storm problem, using only local information. Through a detailed simulation study, we demonstrate that our flooding mechanism improves both the reliability and the efficiency of flooding in MR-MC WMNs.

While the Internet was designed with host-oriented networking applications, recent Internet statistics show that content-oriented traffic has become more and more dominant. Even though content-oriented networking, which tries to resolve this discordance, has received increasing attention, there have been few comprehensive and quantitative studies on how to realize a content-oriented networking architecture. In this paper, we focus on the design alternatives of the content-oriented networking architecture and evaluate their performance: (i) how to locate contents, (ii) how to cache contents, and (iii) how to deliver contents. There are two major infrastructure alternatives in substantiating these mechanisms: a tree and a distributed hash table (DHT).We carry out comprehensive simulation experiments to compare these alternatives in terms of content transfer latency, cache effectiveness, and failure resilience.

The IEEE 802.11 standards support multiple bit rates at the physical layer so that stations can maximize the system performance by controlling the transmission rate responding to the conditions of underlying time-varying channels. This paper proposes a novel scheme, termed as rate adaptation using rate-adaptive acknowledgment (RARA). The key idea of RARA is to regulate the ACK transmission rate as a means to dictate the sender to adjust the data transmission rate. Compared with previous works, the proposed scheme can react quickly to the prevailing conditions by the receiver-based decision while inducing marginal overhead. Simulation results show that the RARA consistently outperforms other rate adaption schemes.

In this paper, we seek to enhance the poor performance of original TCP in wireless multi-hop environments due to the intra-flow contention between TCP-DATA and TCP-ACK packets. Assuming multi-radio multi-channel networks, where each station is equipped with multiple radios and the same number of orthogonal channels, we propose to use virtually different paths with different channel assignments for TCP-DATA and TCP-ACK transmissions. Simulations show that TCP performance can be improved significantly since TCP-DATA and TCP-ACK paths hardly interfere with each other.

Flooding is a mechanism that distributes packets to every node of the network. The flooding mechanism is frequently used in many operations in wireless multi-hop networks. Since flooding exploits hop-by-hop broadcasting that suffers from unreliable transmission and fading, it is hard to achieve the reliability in flooding. As unreliable flooding may lead to a coverage hole, it will have a negative effect upon upper layer protocols. In this paper, we introduce a Reliability Aware Flooding Algorithm (RAFA), which estimates the expected reliability using two-hop topology knowledge. The estimated reliability is used for deciding whether or not to retransmit a packet. Using NS-2 [19] simulator, we show that RAFA achieves the higher reliability than RBP [1] by adjusting the number of retransmissions considering the network topology, regardless of the network topologies, the node density or the number of bottlenecks.

The enormous growth in the use of the IP-based multimedia and other applications has increased the need to use the available communication technologies including satellite and radio links efficiently. These wireless links generally induce high bit error rates and long delays. Moreover, the deployment of IP protocols over these links leads to significant header overhead. IP tunneling mechanisms, widely used in the network security, IPv4-to-IPv6 transition, and mobile networks also have long delay characteristics. This paper studies the behavior of one of the most commonly used Robust Header Compression (ROHC) mechanism over such long delay links and tunnels. We show the impact of long delay, high bit error rate, and packet reordering on ROHC performance. Some of the experiments have been conducted over L2TP tunnel between France and Korea. The results show that ROHC compression can be used over long delay links to reduce header overheads with certain limitations. The results presented in this paper will provide the basis for further designing header compression schemes specifically suited for links and tunnels with long delays.

Multicasting is useful for various applications such as multimedia broadcasting. In current 802.11, multicast frames are sent as broadcast frames at a low transmission rate without any acknowledgement or binary exponential backoff. This naive multicasting mechanism degrades the performance of not only multicast flows but also unicast flows. In this paper, we propose a new multicasting mechanism based on the leader- based approach to improve the legacy multicast transmissions, maintaining coexistence with legacy 802.11 devices. Simulations show that our protocol achieves well-balanced performance in terms of reliability, latency, goodput, and transmission fairness in comprehensive environments.

Finding a reliable and efficient routing path in vehicular ad hoc networks (VANETs) is a challenging issue due to high mobility of vehicles and frequent link breakage. Motivated by this, we propose a robust and efficient routing protocol, called MMR. The contribution of this paper is two-fold: two-level routing and a new routing metric. A routing process of MMR consists of the macro level and the micro level. MMR forwards a packet to an approximate location of the destination at the macro level and then forwards a packet to the exact location of the destination at the micro level. This two-level routing reduces the protocol overhead and improves scalability in terms of the number of nodes. MMR also introduces a new routing metric that reduces the protocol overhead and path breakage by considering velocities of vehicles. Through simulations, we show that MMR improves the routing performance by about 30~40% in highly mobile environments, compared to the existing ad hoc routing protocols such as AODV and GPSR.

The IEEE 802.11e standard supports a direct-link setup (DLS) mechanism optionally to improve the throughput. Using this mechanism, IEEE 802.11e stations in proximity can directly exchange frames with no intervention of an access point. However, extensive simulations reveal the severe unfairness between external and local TCP connections in the IEEE 802.11e DLS mode due to the characteristics of TCP: a window-based flow control mechanism. This paper first analyzes why a fairness problem happens between external and local TCP connections in the IEEE 802.11e DLS mode. Then, we seeks to achieve fairness between them by introducing a novel mechanism dubbed half direct-link setup plus (H-DLS) which differentiates the paths for TCP DATA and ACK packets of local TCP connections. Simulation results reveal that H-DLS achieves the fairness between external and local TCP connections while keeping the aggregate throughput higher than the original IEEE 802.11 infrastructure.

In wireless networks where communications are made over a shared medium, interference and collisions are the primary causes of packet drops. In multi-hop networks such as wireless mesh networks, due to the hidden terminal problem, limiting the effects of collisions and interference is a key in achieving high performance. Typical wireless medium access control protocols perform carrier sensing to avoid collisions. Most research efforts so far has used the binary model when studying carrier sensing and interference; a node is either carrier sensed or not, and a link is either interfered or not. In reality however, there exists a gray zone. Carrier sensing and interference should be represented in continuous values. Using the measurement data from our 802.11a wireless mesh network test-bed, we propose metrics that represent the levels of carrier sensing and interference. Using our metrics, we also propose methods to estimate broadcast throughput and goodput. We evaluate the accuracy of our methods by comparing our models with the measured data. In addition, we investigate the impact of the capture effect on interference.

In this paper, we propose a hybrid query tree protocol that combines a tree based query protocol with a slotted backoff mechanism. The proposed protocol decreases the average identification delay by reducing collisions and idle time. To reduce collisions, we use a 4-ary query tree instead of a binary query tree. To reduce idle time, we introduce a slotted backoff mechanism to reduce the number of unnecessary query commands. For static scenarios of tags, we extended the proposed protocol by adopting two phases. First, inleafqueryphasefor existing tags, the interrogator queriesleaf-nodes directly to reuse query strings in the previous session. Second, inrootqueryphasefor new arriving tags, the interrogator starts the query process from theroof-node. Simulation reveals that the proposed protocol achieves lower identification delay than existing tag collision arbitration protocols regardless of whether tags are mobile or not.

This paper via analysis and simulation revisits the interaction between MAC contention and TCP congestion control over IEEE 802.11 WLANs, misled in the previous efforts. The results reveal that the effective number of contending wireless stations is not proportional to the number of wireless stations with an upstream TCP flow in IEEE 802.11 wireless LANs. Thus, we propose a new scheme called TCP ACK priority (TAP) in which, by allowing an access point to transmit TCP ACKs at the highest priority, the optimal number of competing stations are allowed to contend for media access to utilize link bandwidth efficiently. We use an ns-2 simulator to evaluate the performance of TAP with the IEEE 802.11 DCF. The results show that there is an improvement in network performance without the loss of fairness between upstream TCP flows. The extensions for IEEE 802.11e/n are also considered.

A crucial issue in deploying wireless sensor networks is to perform a sensing task in an area of interest in an energy-efficient manner since sensor nodes have limited energy power. The most practical solution to solve this problem is to use a node scheduling protocol that some sensor nodes stay active to provide sensing service, while the others are inactive for conserving their energy. In this paper, we present a distributed node scheduling protocol, which can maintain sensing coverage required by applications and yet increase network lifetime by turning off some redundant nodes. In order to do this, we use the concept of an effective sensing area (ESA). The ESA of a sensor node refers to the sensing area that is not overlapping with other sensor's sensing area. A sensor node determines whether it will be active or not after calculating its own ESA. The proposed protocol allows sensor nodes to sleep opportunistically while satisfying the required sensing coverage. Through extensive simulation experiments, we have observed significant improvement in terms of network lifetime, which we have compared with the existing protocols.

In vehicular ad hoc networks (VANETs), geographic routing protocols appear to be a fascinating option since they have generally low delay and small routing overhead and GPS devices are becoming affordable. However, we reveal that geographic routing protocols suffer from routing holes when nodes are distributed only on lines such as cars on roads, trains on rails, and ships on courses. To tackle this problem, we propose a novel geographic routing protocol, virtual vertex routing (VVR), which uses the information of the lines. Using graph formulation, we introduce a new concept, the proximity of a vertex (or a virtual vertex). An intermediate node in this proximity performs routing toward the destination by Floyd algorithm. For routing holes, we propose two countermeasures: greedy routing (VVR-GR) and face routing (VVR-FR). The latter can guarantee the packet delivery. Extensive simulations are performed to show that VVR outperforms GPSR and AODV.

Abstract The advent of advanced mobile/wireless systems has been facilitating the battery‐powered mobile computing devices (nodes) to remain always connected to the internet. However, until now, the power‐drain rate of mobile nodes is very high in comparison with the available power of portable batteries. To reduce the energy consumption of mobile nodes, we present an integrated IP paging protocol (IIPP) by integrating the IP‐layer paging protocol based on Mobile IPv4 regional registration (MIPRR) with a power save mechanism. IIPP reduces the frequency of signaling messages between mobile nodes and networks. When not sending or receiving data for a certain time, mobile nodes enter power save mode (PSM), and consume very low power. We formulate analytical models and carry out simulations to evaluate the proposed IIPP. The results show that, compared to MIPRR, IIPP significantly reduces the average power consumption of the mobile node and signaling overheads in the network. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract — The IEEE 802.11 protocol has become the de facto standard in wireless LANs. However, it reveals the unfairness problem between unicast flows and multicast flows since multicast packets are not subject to binary exponential backoff. To prevent a multicast flow from overwhelming the wireless link bandwidth is a crucial issue. This paper seeks to achieve fairness between unicast and multicast flows by introducing Unicast-Friendly Multicast (UFM). The central idea behind the UFM algorithm is to dynamically change the contention window size for multicast packets to limit the bandwidth share of a multicast flow equal to that of a unicast flow. The proposed UFM algorithm adjusts the multicast contention window size depending on the number of competing stations. We present two versions of UFM: the first one calculates the multicast window size by inferring the average contention window size of unicast flows, while the second one maintains the mapping table between the number of competing stations and the corresponding multicast window size given by related analysis. Simulation reveals that both versions of UFM achieve the fairness by providing almost the fair share of bandwidth to each flow regardless of unicast or multicast under the saturated network conditions. I.

International audience

IEEE 802.11 DCF exhibits poor scalability due to the large contention overhead. Therefore, the more the number of stations, the less the aggregate throughput. We propose a two-phase collision avoidance scheme to reduce the collision probability and to enhance the throughput performance. In our proposed scheme, contention among stations is resolved in two phases: SuperSlots and SubSlots. Also, our truncated backoff mechanism increases the throughput by reducing the idle time slots. We analyze the performance of our proposed scheme based on the previous analysis of 802.11 DCF. Both the analysis and simulation results exhibit that our proposed scheme achieves higher throughput than the current IEEE 802.11 backoff mechanism, and this differential increases with the number of stations in the network.

This paper introduces a new split-TCP approach for improving TCP performance over IEEE 802.11-based wireless LANs. TCP over wireless LANs is not aggressive, which is a fundamental reason for poor performance. We propose augmented split-TCP (AS-TCP) to mitigate this problem. Our scheme extends the split-connection approach that divides a connection into two different connections at a split point such as an access point. Using AS-TCP, a mobile host emulates TCP ACK packets using MAC ACK frames, instead of receiving real TCP ACK packets. We compared AS-TCP with both normal TCP and I-TCP (indirect TCP) by simulation. Results show that AS-TCP achieves higher throughput, fairer resource allocation and, in power-saving mode, shorter delays.

IEEE 802.11 MAC protocol in distributed coordination function (DCF) mode is not scalable as the number of contending users increases. In this paper, we propose two new contention resolution schemes to reduce the number of collisions due to a large number of contending users. The first scheme, hybrid DCF (H-DCF), splits the monolithic contention resolution into two phases to enhance scalability. The other scheme, enhanced hybrid DCF (EH-DCF), provides fairness with the current IEEE 802.11 MAC and yet improves the efficiency of contention resolution. The major contribution of our work is to provide inter-operability with the IEEE 802.11 DCF as well as an efficient channel access, unlike the previous works. We conduct comprehensive simulation experiments by using an ns-2 simulator to demonstrate the advantages of these two schemes. The results show that they improve network performance by up to 10~30%, compared to the original IEEE 802.11 DCF. Therefore, H-DCF and EH-DCF can be good candidates for MAC protocols for hotspots where numerous users access wireless LANs intensively

IEEE 802.11 WLAN has been widely accepted throughout the world. However, it has large overhead due to idle backoff slots and frequent collisions depending on the number of nodes. In this paper, we propose a novel medium access control scheme, scheduling-based coordination function (SCF). SCF polls the next station to be serviced by piggybacking. The selection of the next station is based on self-clocked fair queueing (SCFQ) scheduling in a distributed manner. Due to polling, SCF does not suffer from collisions and is efficient owing to the SCFQ scheme. SCF improves the system throughput up to 63.2% compared to IEEE 802.11 DCF. Comprehensive simulation is performed to compare SCF with DCF, PCF, and fast collision resolution (FCR).

In wireless sensor networks (WSNs), reducing energy consumption of resource constrained sensor nodes is one of the most important issues. In this paper, we propose a task aware (TA) MAC protocol, which improves energy efficiency and throughput by introducing a channel access scheme depending on traffic load in WSNs. The amount of traffic load of a sensor node can be estimated by its task activity, where a task is an operation that the sensor node performs based on the schedule set by data dissemination procedures in advance. In addition, the sensor node collects neighbor nodes' task activities and determines its channel access probability using the collected information. Consequently, the sensor node can choose a more suitable channel access probability which is adaptive to its traffic load as well as neighbor's traffic load. We carry out performance analysis using a p-persistent MAC protocol. The results reveal that the TA-MAC protocol exhibits less collisions than the normal p-persistent MAC protocol and thus it achieves energy efficient operations. Also, it can been seen that the TA-MAC protocol improves system throughput compared with other protocols

Mobile IP is the basic solution to provide host mobility, whereas network mobility refers to the concept of collective mobility of a set of nodes. In the simplest scenario, a mobile network moves as a single unit with one mobile router (MR) that connects it to the global Internet. Also, multiple mobile networks can be nested in a hierarchical form, e.g., a wireless personal area network (PAN) in a vehicular network. In a nested mobile network, multiple MRs form a tree hierarchy in which the root MR is called the top-level mobile router (TLMR). Nested mobile networks exhibit the pinball routing problem, which becomes worse in proportion to the number of nested levels in the hierarchy. To solve this problem, we propose a routing optimization scheme using a tree information option (ROTIO) that extends the NEMO basic support protocol. In the ROTIO scheme, each MR in the nested mobile network sends two binding updates (BUs): one to its home agent and the other to the TLMR. The former BU contains the TLMR's home address, while the latter contains routing information between the issuing MR and the TLMR. This alleviates the pinball routing problem significantly. Now, a packet from a correspondent node only needs to visit two transit nodes (the home agents of the MR and the TLMR), regardless of the degree of nesting. Moreover, the ROTIO scheme provides location privacy and mobility transparency. We also extend ROTIO to perform routing between two mobile network nodes inside the same nested mobile network more efficiently and to substantially reduce the disruption when a mobile network hands off.

Mobility support in IEEE 802.11 networks is a challenging issue. Recently, a new scheme, called proactive neighbor caching (PNC), was proposed and adopted as an IEEE standard. The PNC scheme introduces a neighbor graph, which dynamically captures the mobility topology of a wireless network for pre-positioning the context of a mobile host (MH). However, the PNC scheme may result in a significant signaling overhead because the MH's context is propagated to all neighbor access points (APs). We propose a selective neighbor caching (SNC) scheme, which propagates an MH's context to only the selected neighbor APs considering handoff frequencies between APs. When the context transfer is needed, neighbor APs with handoff probabilities equal to or higher than a predefined threshold value are selected. We also derive an optimal threshold value when the target cache hit probability is given. Simulation results reveal that the SNC scheme significantly reduces the signaling overhead while guaranteeing a comparable cache hit probability compared to the PNC scheme.

The number of multi-homed user sites has been rapidly increasing in recent years, where a campus or company network is connected to multiple Internet service providers' networks to improve Internet service reliability. In this paper, we examine the impact of multi-homing via BGP on routing stability and network reliability. More specifically, we compare single-homed prefixes with multi-homed prefixes in terms of the number of routing update messages and the duration of unreachability. Our results show that, on average, single-homed prefixes both generates fewer routing updates than multi-homed prefixes, and provide higher reliability than 97% of multi-homed prefixes (which have a low degree of multi-homing). These results suggest the need to further improve BGP's stability to enable Internet users to gain the expected reliability benefit from multi-homing.

Recently, mobile agents have been proposed for efficient data dissemination in sensor networks. In the traditional client/server-based computing architecture, data at multiple sources is transferred to a destination; whereas, a task-specific executable code traverses the relevant sources to gather data in the mobile-agent based computing paradigm. As described in Hairong Qi, et al. (2003), many inherent advantages (e.g. scalability, extensibility, energy awareness, reliability) of the mobile agent architecture make it more suitable for sensor networks than the client/server architecture. In this paper, a mobile agent is exploited in three levels (e.g. node level, task level, and combined task level) to reduce the information redundancy and communication overhead.

To join an IP network and communicate with others, a node needs to be configured either manually by an administrator or automatically through a DHCP server. However, the former method is impractical for large networks, while the latter is infeasible in the case of a mobile ad hoc network due to the mobility of the nodes. This paper introduces two distributed IP address auto-configuration mechanisms for mobile ad hoc networks, namely (a) RADA (random address allocation) and (b) LiA (linear allocation). RADA is based on random IP address selection, while LiA linearly assigns new addresses by utilizing the current maximum IP address value. We have also introduced an improved version of LiA, known as LiACR (linear allocation with collision resolution), which reduces control overhead. Then, we discuss extensions of these mechanisms capable of handling network partitioning and merging. Performance evaluations of RADA, LiA and LiACR were conducted through simulation. The results related to address allocation time and control overhead are presented and compared.

Although hierarchical mobile IPv6 (HMIPv6) can reduce the signaling overhead and the handoff latency, it results in the non-optimal local routing problem when two mobile nodes communicate in the same mobility anchor point domain. To address this problem, we propose an adaptive local route optimization (ALRO) scheme. The ALRO scheme chooses either the global route optimization scheme or the local route optimization scheme depending on the session-to-mobility ratio (SMR). Based on the proposed analytical model, we find the optimal SMR threshold at which the ALRO scheme shows the best performance. Numerical results demonstrate that the ALRO scheme shows a good performance in terms of the total cost, session delivery time, and session disruption time.

By means of network mobility (NEMO) support, users can organize their various communication devices into a network, called a mobile network. In a mobile network, the mobile router provides the connectivity to the Internet and mobility management transparency for the rest of the mobile nodes in the mobile network. So, it is important for the mobile router to assure reliable communications and a high data rate for the group of nodes behind it. In support of broadband wireless communications, the use of multiple mobile routers would allow the transfer of large volumes of data to a group of mobile nodes. This paper addresses the protocol issues arising from the use of multiple mobile routers, and analyzes the influence of mobility on load sharing and session preservation when there are multiple mobile routers. Simulation results with different configurations show that session preservation and load sharing schemes are influenced by application mobility behavior and wireless access technologies.

In this paper, we propose a mobility-based load control scheme, which consists of two sub-algorithms: (1) a threshold-based admission control algorithm; and (2) a session-to-mobility ratio (SMR) based replacement algorithm. Here the SMR is defined as a ratio of the session arrival rate to the handoff rate. When the number of mobile nodes (MNs) at a mobile anchor point (MAP) reaches to the full capacity, the MAP replaces an existing MN at the MAP, whose SMR is high, with an MN that just requests a binding update. The replaced MN is redirected to its home agent. We analyze the proposed load control scheme using the Markov chain model in terms of the new MN blocking probability and the ongoing MN dropping probability. By combining the threshold-based admission control with the SMR-based replacement, the above probabilities are lowered significantly compared to the threshold-based admission control alone.

Hierarchical mobile IPv6 (HMIPv6) is an enhanced mobile IPv6 in order to reduce signaling overhead and to support seamless handoff in IP-based wireless/mobile networks. To support more scalable services, HMIPv6 can be organized as a multilevel hierarchy architecture (i.e, tree structure). However, since the multi-level HMIPv6 results in additional packet processing overhead, it is necessary to consider the overall cost and to find the optimal level to minimize the overall cost. In this paper, we investigate this problem, namely the design of a multi-level HMIPv6 with optimal hierarchy. To do this, we formulate the location update cost and the packet delivery cost in the multi-level HMIPv6. Based on the formulated cost functions, we present the optimal hierarchy level in the multi-level HMIPv6 to minimize the total cost. In addition, we investigate the effects of session-to-mobility ratio (SMR) on the total cost and the optimal hierarchy. The numerical results, which show various relationships among network size, optimal hierarchy, and SMR, can be utilized to design an optimal HMIPv6 network.

Security is very important during transmission of data in wireless networks. Bit errors frequently occur in wireless networks, which consequently create critical data losses as encrypted data is decrypted. The relation between bit errors and serviced quality after decryption about several encryption algorithms supported by IPv6 was researched. RC4 shows a higher PSNR than DES in CBC mode and AES in CBC mode when JPEG and MPEG multimedia data is transmitted.

The integration of 3G networks and WLAN as complementary has begun to attract much attention in industry as well as academia. This topic is becoming a burning issue, and one of the key questions which it raises is how to support a seamless vertical handoff. This paper introduces a new interface selection algorithm for energy-efficient vertical handoff in tightly coupled systems capable of supporting seamless handoff. Our proposed scheme, Wise Interface Selection (WISE) switches the active network interface, after taking into consideration the characteristics of the network interface cards and the current level of data traffic, with the cooperation of the mobile terminals and network. Interface switching operates independently on both the downlink and the uplink for the purpose of energy conservation. We show through simulation that less energy is consumed with WISE than when only a 3G network or WLAN interface is used, resulting in a longer lifetime for the mobile terminals. In the case of TCP connections, additional throughput gain can also be obtained.

Recently, the radio frequency identification (RFID) technology has gained significant attention. One of the important performance issues in RFID systems is to resolve the collision among responses from RFID tags from the viewpoint of wireless media access control. We consider two kinds of smart antenna systems to enhance the RFID tag reading rate, namely the adaptive array antenna and the multiple-input multiple-output (MIMO) antenna. We consider passive tags that are operating without battery. We evaluate how much performance can be improved by employing smart antennas in the cases of the binary tree splitting algorithm and the Slotted-Aloha algorithm.

We evaluate the performance of IP paging with power save mechanism by formulating an analytical model and carrying out simulation study of integrated IP paging protocol (HPP) that integrates both the paging and power save functionality in IP layer. The results show that, compared to the mobile IP regional registration, the UPP significantly reduces the average power consumption of a mobile node and the signaling load in the access networks, while providing link layer independent mobility and power management functions.

Recently, IEEE 802.11 wireless networks have been widely deployed in public areas for mobile Internet services. In the public wireless LAN systems, paging function is necessary to support various advanced services (e.g. voice over IP and message applications) and to provide efficient power management scheme. In next-generation mobile networks, the so-called all-IP networks, the paging function will be supported in the IP layer (i.e. IP paging). When IP paging protocol is deployed in IEEE 802.11 wireless networks, it may utilize the power saving mechanism supported in the IEEE 802.11 standard for more efficient power management. However, since the current power saving mechanism is based on a periodical wake-up mechanism with a fixed interval, it is difficult to optimize the power saving performance. In this paper, we analyze the performance of IP paging protocol over IEEE 802.11 power saving mode (PSM). We define a wake-up cost and a paging delay cost. Then, we study the effect of varying the length of the wake-up interval and the session arrival rate. In addition, we analyze the distribution of the session blocking probability due to the coarse-grained wake-up interval. Also, we investigate the optimal wake-up interval to minimize the total cost through simulations. These results indicate that it is necessary to find the optimal wake-up interval in order to minimize the total cost while satisfying the given paging delay constraints.

Next-generation wireless/mobile networks will be IP-based cellular networks integrating Internet with the existing cellular networks. Recently, hierarchical mobile IPv6 (HMIPv6) was proposed by the Internet engineering task force (IETF) for efficient mobility management. HMIPv6 reduces the amount of signaling and improves the performance of MIPv6 in terms of handover latency. Although HMIPv6 is an efficient scheme, the performance of wireless networks is highly dependent on various system parameters such as user mobility model, packet arrival pattern, etc. Therefore, it is essential to analyze the network performance when HMIPv6 is deployed in IP-based cellular networks. In this paper, we propose an analytic model for the performance analysis of HMIPv6 in IP-based cellular networks, which is based on the random walk mobility model. Based on this analytic model, we formulate location update cost and packet delivery cost. Then, we analyze the impact of cell residence time on the location update cost and the impact of user population on the packet delivery cost. Also, we investigate the variation in the total cost as the relative session size and the MAP domain size are changed. As a result, we present various analytical results in different environments.

In this paper, we propose a novel technique for reducing the energy consumption in idle mode. Our proposed technique called the network capacity adaptation derives an effective network capacity required by a given application and logically slows down the network capacity when the traffic load is low. By slowing down the logical network capacity, the neighboring mobile stations can stay longer in the power-off mode, significantly saving the energy consumed in idle mode.

Wireless local area network (LAN) has become popular due to the capability of supporting high data rates in ubiquitous computing. These high data rates are possible through new modulation schemes that are optimized for channel conditions. Especially, IEEE 802.11b supports the various data rates, 11 Mbps, 5.5 Mbps, 2 Mbps and 1 Mbps according to the channel conditions between the access point (AP) and the mobile station. The coverage area supported by the high data rate such as 11 Mbps is very small. However, the lower data rate increases the coverage area, thus the change of data rate can overcome this coverage problem of the high data rate. There are many wireless packet scheduling and buffer management algorithms, but they assume a wireless channel supporting only single base-rate and hardly take advantage of high data rate when multiple data rates are possible. In this paper, we propose the new queue management algorithm in order to utilize high data rate efficiently in the current wireless LAN. Basically, the proposed queue management algorithm manages the priority queue of packets, where packet with shorter transmission time has higher priority, since the transmission time is highly dependent on the available data-rate to the mobile station. We show our suggested algorithm achieves high throughput through the simulation in based in wireless LAN environments based on the IEEE 802.11b.

This paper proposes a new optical path restoration method for wavelength division multiplexing (WDM) networks. In the method, the protection path is established by connecting several sub-lightpaths from the source node to the destination node of the original working lightpath, as opposed to conventional path restoration where a single protection lightpath between the source-destination pair performs restoration. The set of one or more consecutive lightpaths to connect a source-destination pair is called semi-lightpath. The semi-lightpath based restoration provides enhanced flexibility in protection path provisioning and relieves the cost of spare capacity reservation and wavelength conversion at intermediate optical cross-connect nodes. In terms of spare capacity utilization, our method shows substantial reduction of spare capacity overhead compared with dedicated path restoration in all optical networks without wavelength conversion, and shows similar capacity efficiency compared with shared path restoration in opaque networks with full wavelength conversion capability.

A traffic engineering problem consists of setting up paths between the edge nodes of the network to meet traffic demands while optimizing the network performance. It is known that total traffic throughput in a network, hence the resource utilization, can be maximized if the traffic demand is split over multiple paths. However, the problem formulation and practical algorithms, which calculate the paths and the traffic split ratio taking the route constraints or policies into consideration, have not been much touched. This paper proposes practical algorithms that find near optimal paths satisfying the given traffic demand under constraints such as maximum hop count, and preferred or not-preferred node/link list. The mixed integer programming formulation also calculates the traffic split ratio for the multiple paths. The problems are solved with the split ratio of continuous or discrete values. However, the split ratio solved with discrete values (0.1, 0.2 etc.) are more suitable for easy implementation at the network nodes. The proposed algorithms are applied to the multiprotocol label switching (MPLS) that permits explicit path setup. The paths and split ratio are calculated off-line, and passed to MPLS edge routers for explicit label-switched path (LSP) setup. The proposed schemes are tested in a large-scale fictitious backbone network. The experiment results show that the proposed algorithms are fast and superior to the conventional shortest path algorithm in terms of maximum link utilization, total traffic volume, and number of required LSPs.

This paper presents a new traffic engineering technique for dynamic constrained multicast routing, where the routing request of traffic arrives one-by-one. The objective we adopted is to minimize the maximum of link utilization. Although this traffic engineering is useful to relax the most heavily congested link in the Internet backbone, the total network resources, i.e. sum of link bandwidth consumed, could be wasted when the acquired path is larger (in terms of number of hops) than the conventional shortest path. Accordingly we find a multicast tree for routing request that satisfies the hop-count constraint. We formulate this problem as a mixed-integer programming problem and propose a new heuristic algorithm to find a multicast tree for multicast routing request. The presented heuristic algorithm uses the link-state information, i.e. link utilization, for multicast tree selection and is amenable to distributed implementation. The extensive simulation results show that the proposed traffic engineering technique and heuristic algorithm efficiently minimize the maximum of link utilization better than the shortest path.

The design of a wireless local area network (WLAN) has an important issue of determining the optimal placement of access points (AP) and assignment of channels to them. WLAN services in the outdoor as well as indoor environments should be designed in order to achieve the maximum coverage and throughput. To provide the maximum coverage for WLAN service areas, AP should be installed such that the sum of signal measured at each traffic demand point is maximized. However, as users connected to an AP share wireless channel bandwidth with others in the same AP, AP placement should be carefully decided to maximize the throughput by considering load balancing among AP and channel interference for the user traffic demand. In this paper, therefore, we propose an approach of optimizing AP placement and channel assignment in WLAN by formulating an optimal integer linear programming (ILP) problem. The optimization objective is to minimize the maximum of channel utilization, which qualitatively represents congestion at the hot spot in WLAN service areas. It is seen from the simulation results that the proposed method finds the optimal AP placement and channels which minimize the maximum of channel utilization.

Existing routing protocols for mobile ad hoc networks assume that all nodes have the same radio transmission range. In other words, the mobile ad hoc network has symmetric links, which means that two neighboring nodes A and B are within the transmission range of one another. However, since nodes consume battery power independently according to their computing and communication load, there exist asymmetric links, which means that node A is within node B's transmission range, but not vice versa. In this paper, two approaches are presented to support routing in the existence of asymmetric links: GAHA (GPS-based Hop-by-hop Acknowledgment) and GAPA (GPS-based Passive Acknowledgment) schemes. Both GAHA and GAPA can be applied to any routing protocols by utilizing GPS (Global Positioning System) location information. Simulation results reveal that both GAHA and GAPA protocols cope well in the presence of asymmetric wireless links and nodes' mobility.

The existing routing protocols in mobile ad hoc networks assume that all nodes have the same transmission range. In other words, the mobile ad hoc network has only symmetric links. However, since nodes consume battery power independently according to their computing and communication load, there exist asymmetric links, which means that node A is within node B's transmission range, but not vice versa. This paper present two protocols that accommodate asymmetric links: link-level and end-to-end Approaches. The link-level approach can be applied to any routing protocols by utilizing GPS(Global Positioning System) location information of nodes at link level. On the other hand, the end-to-end approach does not need GPS devices and employs dual paths between source and destination. Simulation results reveal that these protocols cope well with ad hoc network having asymmetric wireless links under the presence of mobility.

Multipath routing employs multiple parallel paths between a traffic source and destination in order to relax the most heavily congested link in the Internet backbone. A large bandwidth path can be easily set up too. Although multipath routing is useful, the total network resources, i.e. sum of link bandwidths consumed, could be wasted when the acquired path is larger(in terms of number of hops) than the conventional shortest path. In addition, even though we can accommodate more traffic by establishing more paths between the same node pair, it is advised to limit the number of paths for practical reasons such as manageability. This paper presents a heuristic algorithm for hop-count and path count constrained dynamic multipath routing. The objective we adopted in this paper is to minimize the maximum of link utilization. We also obtain the traffic split ratio among the paths, for routers based on traffic partitioning by hashing at the flow level. The extensive simulation results show that the proposed algorithm always minimizes the maximum of link utilization and reduces the number of blocked requests.

Reliable data transmission over a wireless multi-hop network, called the ad hoc network, has proven to be non-trivial. The TCP (transmission control protocol), a widely used end-to-end reliable transport protocol in a wired network, is not entirely suitable when applied to a wireless ad hoc network due to TCP's congestion control schemes. In particular, the TCP at the source considers the network as congested when detecting packet losses or timeouts. However, in a wireless ad hoc network when a route disconnection occurs because of node movement, the network mistakes this as a congestion. Therefore, the conventional TCP congestion control mechanism cannot be applied, because a route disconnection must be handled differently from a network congestion. We propose a new mechanism that improves the TCP performance in a wireless ad hoc network where each node can buffer packets during a route disconnection and reestablishment. Additionally, we incorporate new measures to deal with the reliable transmission of important control messages. Our simulation results further confirmed these advantages.

The existing routing protocols in mobile ad hoc networks assume that all the nodes have the same transmission range. In other words, the mobile ad hoc network has only symmetric links, which means that two neighboring nodes A and B are within the transmission range of one another. However, since nodes consume battery power independently according to their computing and communication load, there exist asymmetric links, which means that node A is within node B's transmission range, but not vice versa. In this paper, to cope with asymmetric links, a new routing protocol based on source-initiated on-demand routing (called RODA-routing protocol with dual paths to support asymmetric links) is presented. In order to perform route maintenance in an efficient manner, dual paths-forward (source to receiver) and backward (receiver to source) paths-are used to send and receive data packets. In addition, a timer mechanism is introduced to deal with simultaneous and consecutive broken links on both forward and backward paths. Simulation results reveal that RODA copes well with an ad hoc network having asymmetric wireless links under the presence of mobility.

There is a growing interest in deploying multimedia services in mobile cellular networks. Call admission control (CAC) is a key factor in quality of service (QoS) provisioning for these services. We propose a CAC which maximizes the revenue by determining the call admission decisions for each state. A semi-Markov decision process is employed to model the cellular system. Also, the QoS requirement such as the handoff dropping probability is taken into consideration. Simulations reveal that our CAC outperforms the upper limit CAC while satisfying the QoS requirements.

Due to scarce radio resources (e.g., wireless link bandwidth), the cell size is likely to become smaller to increase the frequency reuse ratio, especially in next generation mobile cellular networks. In this scenario, the analysis of handoff traffic is crucial for adequate QoS provisioning. With the assumption that incoming handoff traffic into a cell is equivalent to outgoing handoff traffic from the cell, we propose an iterative computation technique to analyze handoff traffic approximately. The iterative relaxation method is employed to calculate the steady state probabilities. The call blocking probability and the handoff dropping probability are accordingly obtained. We conduct the approximate analysis of handoff traffic in the case of trunk reservation call admission policy and compare the results with those of simulation experiments.

Recently there is a growing interest in adaptive multimedia networking where the bandwidth of an ongoing multimedia call is variable. In this paper, we propose a measurement-based call admission control (CAC) which guarantees the upper bound of the call degradation probability defined herein. Our CAC measures the state of the cellular system in a distributed manner and reflects the observed history of the system on making call admission decisions. Also, a bandwidth adaptation algorithm to minimize the call degradation probability is presented. Simulations reveal that our CAC algorithm outperforms the upper limit CAC algorithm while maintaining quality of service.

Survivability is one of the important issues in broadband networks, since even a single network element failure may cause a serious amount of data loss. There have been two main approaches for connection restoration: dynamic approach and backup approach. We discuss the trade-offs between the two approaches and propose a new restoration mechanism that centers around the concept of the virtual backup network, which provides backup path sharing as well as spare bandwidth sharing. The proposed mechanism can take advantage of the two existing approaches together with special interests in resource efficiency and routing flexibility.

We present a distributed multicast algorithm for constructing minimum cost multicast trees with delay constraints. The proposed algorithm, which provides multicasting and guaranteed end-to-end delay bound at the network layer, is also designed to find a reduced cost routing tree. The proposed algorithm requires limited network state information and the routing tree is computed through a single round of message exchanges between network nodes. We prove the algorithm's correctness by showing that it is always capable of constructing a delay constrained multicast tree, if one exists. The algorithm is verified by simulation, and it is shown that it exhibits superior performance compared to existing ones for the tree cost measure.

To date, various connection rerouting methods for connection-oriented mobile network services have been proposed. The previous methods, however, are limited to specific topologies or environments. In this paper, we propose the CI (Connection Information)-based rerouting widely applicable to various connection-oriented mobile network. This method requires neither a specific topology nor a complex connection, enables fast rerouting, takes a good trade-off between rerouting simplicity and route optimality, and can be extended easily.

To date, various connection rerouting methods for connection-oriented mobile network services have been proposed. The previous methods, however, are limited to specific topologies or environments. In this paper, we propose CI(Connection Information)-based rerouting widely applicable to various connection-oriented mobile networks. This method requires neither a specific topology nor a complex connection, guarantees fast rerouting, and takes a good trade-off between rerouting simplicity and route optimality. These features make the method adequate for general application to various connection-oriented mobile networks.

Multimedia multiuser applications such as computer supported cooperative working, desktop multimedia conferencing, and distance education require more complex and structured communication services from the underlying communication platform than conventional applications. The call model of the communication platform defines how the underlying basic data transport objects can be structured to support more complex communication services, and how the structured objects can be managed in a consistent manner by the applications. In this paper, we present a new call model for multimedia multiuser communication platform, based on the analysis of communication requirements for diverse applications. Our call model provides better structuring capability than the existing call models, and the communication platform based on the call model will support present and future complex multimedia multiuser applications more efficiently. Detailed call control operations are also presented in this paper.