Computer Communications

Published by Elsevier
Online ISSN: 0140-3664
Publications
Article
Over the last decade a large number of routing protocols has been designed for achieving energy efficiency in data collecting wireless sensor networks. The drawbacks of using a static sink are well known. It has been argued in the literature that a mobile sink may improve the energy dissipation compared to a static one. Some authors focus on minimizing Emax, the maximum energy dissipation of any single node in the network, while others aim at minimizing Ebar, the average energy dissipation over all nodes. In our paper we take a more holistic view, considering both Emax and Ebar.
 
Conference Paper
IEEE 802.15.4 is a popular choice for MAC/PHY protocols in low power and low data rate wireless sensor networks. In this paper, we develop a stochastic model for the beaconless operation of IEEE 802.15.4 MAC protocol. Given the number of nodes competing for channel access and their packet generation rates, the model predicts the packet loss probability and the packet latency. We compared the model predictions with NS2 simulation results and found an excellent match between the two for a wide range of the packet generation rates and the number of competing nodes in the network.
 
Conference Paper
This paper explores and proposes the use of open programmable router technologies to achieve dynamic configuration, adaptation and management of network entities. The objective is to provide highly dynamic and flexible edge router technology to support the interconnection between emerging short range wireless technologies such as WPANs and IP based networks. To improve current software based edge router designs, the paper merges the Click framework (an open source software architecture for the forwarding plane) and the Forwarding and Control Element Separation (ForCES) principle. The proposed architecture is implemented on a real testbed based on standard PCs and open source operating systems. Results on achievable performance using these software based solutions and Click are reported. The impact on traffic flows and applications in terms of packet losses and delays is evaluated. q 2005 Elsevier B.V. All rights reserved.
 
Conference Paper
Many enterprises install multiple access links for fault tolerance or bandwidth enlargement. Dispatching connections through good links is the ultimate goal in utilizing multiple access links. The traditional dispatching method is only based on the condition of the access links to ISPs. It may achieve fair utilization of the access links but poor performance on connection throughput. In this work, we propose a new approach to maximize the per-connection end-to-end throughput by the on-the-fly round trip time (RTT) probing mechanism. The RTTs through all possible links are probed by duplicating the SYN packet during the three way handshaking stage of a TCP connection. Combined with the statistical packet loss ratio and the passively collected link metrics, our algorithm can real-time select a link which provides the maximum throughput for the TCP connection. The experiment results show that the accuracy of choosing the best outgoing access link is over 71%. If the second best link is chosen, it is usually very close to the best, thus achieving over 89% of the maximum possible throughput. The average per-connection throughput for our algorithm and the traditional round-robin algorithm is 94% vs. 69%.
 
Conference Paper
Delivering multicast data using application layer approaches offers different advantages, as group members communicate using so-called overlay networks. These consist of a multicast group's members connected by unicast tunnels. Since existing approaches for application layer delivery of multicast data in mobile ad hoc networks (short MANETs) only deal with routing but not with error recovery, this paper evaluates tailored mechanisms for handling packet losses and congested networks. Although illustrated at the example of a specific protocol, the mechanisms may be applied to arbitrary overlays. This paper also investigates how application layer functionality based on overlay networks can turn existing multicast routing protocols (like ODMRP, M-AODV,…) into (almost) reliable transport protocols.
 
Conference Paper
In near video-on-demand (near-VoD), requests for a video title are grouped together (i.e. batched) and are served with a single multicast stream, thereby increasing the number of concurrent users which can be supported by the system. Since users may not be able to tolerate the delay incurred by batching and hence cancel their requests, a batching policy should be designed so as to achieve low user loss and high revenue (given by the total pay-per-view collected over a long period of time across all movies). We propose an adaptive batching policy which offers users low delay at low arrival rate, and gates the allocation of the channels at high rate. Such adaptivity is achieved by the use of a simple “token-tray” (TT) scheme which governs when a stream may be allocated to a movie. In assigning a movie to a stream, we propose a weight function which depends on the user queuing-time and its pay-per-view (hence the term “weighted queuing-time”) (WQT). By comparing our batching policy (TT/WQT) with a number of traditional ones (FCFS, forced-wait, batch-size-based scheme, etc.), our scheme is shown to achieve the highest revenue and lowest loss rate even when the arrival rate changes, with the user loss rate across the movies being fairly uniform, and the user delay being fairly low even at high arrival rate
 
Conference Paper
We present an admission control scheme for real-time VBR traffic. The deterministic guarantee on the end-to-end delay bound is adopted as the measure of quality-of-service (QoS). The network environment of our admission control algorithm is the connection-oriented network, in which every network node uses the rate-controlled service (RCS) discipline based on the earliest deadline first (EDF) scheduling policy. Unlike the previous studies, this paper focuses on designing an efficient bandwidth allocation scheme, in which the service curve and the spare capacity curve are two important terminologies employed. Experiments using the parameters derived from some real video traces show that our algorithm performs better than previous ones in terms of both the network bandwidth utilization and the computational time needed
 
Conference Paper
The decisions of connection admission in ATM networks should be made in real time through the use of a fast algorithm. Since it is difficult to construct an accurate model for the multiplexed traffic, approximation of the multiplexed load is necessary. We focus on a dynamic CAC (connection admission control) algorithm as a different approach, in which admission control decisions are made based on network measurements. The algorithm observes the traffic through a moving window and the window size is recomputed from the measured cell loss. This approach also makes it possible to reallocate network resources (bandwidth and buffers) for multiple traffic classes. The performance of the proposed method is analyzed by means of simulated tests
 
Conference Paper
Data broadcast has become a promising solution for information dissemination in the wireless environment. In this system, the average expected delay (aed) depends on the broadcast schedule because different data items may have different popularities and there are multiple broadcast channels for current delivery. In this paper, a restricted dynamic programming approach to minimize the aed is proposed to partition data items over multiple channels near optimally. To reduce costs in dynamic programming, for each partition, we predict a possible location which may be very close to the optimal cut by using a low bound of aed for given items among given channels. Thus, the search space in dynamic programming can be restricted to the interval around the found cut point and only takes O(NlogK) time. Moreover, a valley approximation algorithm is performed to improve the aed. Simulation results show that, the hit rate obtained by our algorithm is higher than 95% and it also outperforms the existing algorithm 200%.
 
Conference Paper
From manufacturers, distributors, and retailers of consumer goods to government departments, enterprises of all kinds are gearing up to use RFID technology to increase the visibility of goods and assets within their supply chain and on their premises. However, RFID technology alone lacks the capability to track the location of items once they are moved within a facility. We present a prototype automatic location sensing system that combines RFID technology and off-the-shelf Wi-Fi based continuous positioning technology for tracking RFID-tagged assets. Our prototype system employs a robot, with an attached RFID reader, which periodically surveys the space, associating items it detects with its own location determined with the Wi-Fi positioning system. We propose four algorithms that combine the detected tag's reading with previous samples to refine its location. Our experiments have shown that our positioning algorithms can bring a two to three fold improvement over the positional accuracy limitations in both the RFID reader and the positioning technology.
 
Conference Paper
Orthogonal variable spreading factor (OVSF) codes have been proposed as the channelization codes used in the wideband CDMA access technology of IMT-2000. OVSF codes have the advantage of supporting variable bit rate services, which is important to emerging multimedia applications. The objective of OVSF code assignment algorithm is to minimize the probability of code request denial due to inappropriate resource allocation. In this paper, we propose an efficient OVSF code assignment scheme that utilizes multiple Rake combiners in user equipments. Our approach finds in constant time all feasible codewords for any particular request, trying to minimize both rate wastage and code fragments. The simulation result shows that our scheme outperforms previous work in the probability of request denial. The code management overhead is also minimal in our scheme.
 
Conference Paper
Fixed channel assignment in wireless communication networks is an important combinatorial optimization problem that must be solved for application problems. Since it is NP-hard, many different heuristics are proposed for its solution. We consider two types of interference conditions for channel assignment: a co-channel interference within distance of two cells and a adjacent channel interference within the same and the adjacent cells. Our goal is to minimize or disallow these two types of interference in order to achieve optimal channel assignment. First we present our recursive search algorithm together with the neighborhood improvement structure. Then we minimize or disallow these two types of interference in order to achieve optimal channel assignment. We suggest a general approach combining several important heuristics. Our experimental results show that our algorithm improves over known approaches.
 
Conference Paper
Presents a new scheme that enables destination nodes in a slotted shared medium network to release some received slots, hence making them available for reuse by other downstream nodes in the network. This scheme ensures a significant increase in the effective capacity of the network without any noticeable degradation in node processing delays, or increase of node complexity
 
Conference Paper
This paper introduces a new feature of IPv6 called an extension header. An extension header is located between the IPV6 header and the TCP header and offers new possibilities for IP over ATM signalling and high capacity allocation in backbone networks. In IPV6 it is possible to insert an arbitrary number of extension headers between the Internet header and the payload
 
Conference Paper
Two attacks are given to show that the identity-based signature scheme proposed by C. C. Chang and C. H. Lin (1991) based upon Rabin's public key cryptosystem is not secure enough. One of the attacks is based on the conspiracy of two users in the system while the other can be performed by anyone alone. It is shown that, in this second attack, the scheme can be broken by anyone (not necessarily a user in the system) who has the ability to observe the communications between the signer and the receiver
 
Conference Paper
A large fraction of traffic that the future B-ISDN will probably transport is made up of real-time services with stringent delay and delay jitter requirements. Since ATM networks do not provide time transparent links, a delay equalisation has to be provided in the adaptation layer or in user equipment. In this paper we first propose an analytical model that allows the evaluation of the end-to-end delay and of the relevant jitter (the delay that we consider is the one suffered in the network queueing systems plus the time needed to transmit a cell but not the propagation delay; the latter can be trivially added to the former); then we focus on the dimensioning of play-out buffers. The proposed model is validated with simulation results and we found a good agreement between analytical and simulation results. To make the study analytically tractable we use rather simple traffic source models and we make suitable simplifying assumptions. These assumptions are fairly general but the source models are still far from representing accurately certain kinds of real traffic. For this reason we carry out also an additional simulation study (supported by some analytical arguments), by using real experimental MPEG, LAN and Internet traffic traces, to assess the system performance in real scenarios
 
Conference Paper
The authors study the effect of channel sharing on the performance of multihop lightwave networks when channel sharing is achieved by using a time-division multiple-access (TDMA) technique. They present a result which gives an upper bound for the throughput that can be achieved with any virtual topology that can be established with N stations assuming that the traffic distribution is uniform and that all virtual links have the same capacity. Using this result they determine the optimal degree of channel sharing that maximizes throughput. They also determine the optimal degree of channel sharing when the criterion is to maximize the network power, which is defined as a ratio of throughput and delay
 
Conference Paper
Data gathering is a basic activity of many wireless sen- sor network applications. We propose a novel collaborative data gathering approach utilizing data co­occurrence, which is different from data correlation. Our approach of- fers a trade-off between communication costs of data gathering versus errors at estimating the sensor measurements at the base station, by having sensors with co­occurring measurements alternate in transmitting such measurements to the base station, and having the base station make infer- ences about sensor measurements utilizing only the trans- mitted data. We describe two effective methods for in- network detecting measurements co-occurrence among sen- sors, an efficient protocol for scheduling the transmission of measurements, and a simple algorithm for measurement inference. Our simulation results on synthetic and real datasets show a substantial (up to 65%) reduction on the communication costs of data gathering with few number of inference errors at the base station.
 
Conference Paper
By combining the transmit diversity and space multiplexing, the multi-layer multiple-input multiple-output orthogonal frequency division multiplexing (multi-layer MIMO-OFDM) system can exploit the potentials of both techniques. The transmit antennas are divided into several layers and each layer is encoded by a certain multi-antenna coding. The antennas transmit OFDM signals in order to deal with frequency-selective fading. In addition to exhaustive detection which applies the same detection at each subcarrier independently, we exploit the subcarrier correlation to develop a subcarrier-grouping based low-complexity detection scheme. The subcarriers bound into the same group share the same layer detection order which is obtained by the post-nulling signal power comparison at the center subcarrier of that group. The simulation results show that compared with exhaustive detection, the proposed low-complexity detection scheme is capable of reducing 50.7% complexity with only 0.8dB performance degradation for 6x6 system, and reducing 60.7% complexity with about 1.0dB performance degradation for 8x8 system, respectively.
 
Conference Paper
This paper develops an efficient method based on traffic flow distribution and splitting for traffic engineering in the MPLS networks. We define flow distribution as selecting one of the available label switch paths (LSPs) to carry one aggregated traffic flow. Flow splitting is, however, the mechanism designed for multiple parallel LSPs to share one single aggregated flow. Our studies show that flow distribution and flow splitting approaches readily solve the routing problems such as bottleneck and mismatch problems. An algorithm based on network bandwidth utilization is also proposed to integrate both approaches. The simulation results at the end of the paper demonstrate the effectiveness of the proposed approaches.
 
Conference Paper
Online social networks such as Facebook, MySpace, and Orkut store large amounts of sensitive user data. While a user can legitimately assume that a social network provider adheres to strict privacy standards, we argue that it is unwise to trust third-party applications on these platforms in the same way. Although the social network provider would be in the best position to implement fine-grained access control for third party applications directly into the platform, existing mechanisms are not convincing. Therefore, we introduce PoX, an extension for Facebook that makes all requests for private data explicit to the user and allows her to exert fine-grained access control over what profile data can be accessed by individual applications. By leveraging a client-side proxy that executes in the user's web browser, data requests can be relayed to Facebook without forcing the user to trust additional third parties. Of course, the presented system is backwards compatible and transparently falls back to the original behavior if a client does not support our system. Thus, we consider PoX to be a readily available alternative for privacy-aware users that do not want to wait for privacy-relevant improvements to be implemented by Facebook itself.
 
Conference Paper
It is important that applications deployed in wireless networks be robust enough to accommodate different kinds of data losses due to link errors, connection re-routing, and network congestion. A scheme to improve the robustness of MPEG based video applications is proposed. Under this scheme, the packet size at the sender is optimized to the MPEG system layer unit size to enable fast recovery of the time stamps. The receiver buffers the data packets for re-playing during packet losses, preserves useful time stamps for synchronisation, and re-synchronises the decoder when packet loss occurs. This involves no feedback and results in faster recovery of critical timing information for video decoding. The proposed method has been implemented on a video application based on MPEG-I over an ATM network. The experiments show that the proposed technique is very effective when there is deterministic/random packet losses with burst size less than 21. The method is equally applicable to video applications based on MPEG-II program stream and, to wireless Internet
 
Conference Paper
The critical parameter in a window flow control scheme is the window size, which represents the maximum number of packets that can be in transit at a time. In this paper, we consider the problem of selecting the optimum window size in high-speed data networks. A self-optimizing method is proposed to adapt the window size to network conditions. The scheme employs a cross-correlation technique for process identification where the perturbation signal is random. Simulation results are presented for the isarithmic flow control to show the convergence rate and stability characteristics of the self-optimizing scheme.
 
Conference Paper
Following the development of TCP Vegas, the performance comparison between TCP Reno and TCP Vegas has not been discussed thoroughly. The discussion of the revised TCP version, TCP Vegas, remains insufficient to decide whether or not to use it. This paper attempts to compare the performance, throughput and fairness, of Reno and Vegas in the network environments with homogeneous and heterogeneous versions of TCP. Results in this study indicate that while TCP Vegas obtains better throughput and fairness in homogeneous cases, it fails to outperform Reno in heterogeneous cases. This phenomenon prevents users from adopting TCP Vegas despite its better performance
 
Article
As organizations have become increasingly dependent on their networked computing environments, the importance of effective network management has become a key element in the success of those networks. A flurry of activity in the network management field has resulted in a number of different standards efforts taking place concurrently, and different manufactures adopting different standards for current products. The standards activities of most importance to one company, 3Com UK Ltd, are outlined, and the possibilities for future product development are discussed, particularly with reference to 3Com/IBM's recent Heterogeneous LAN Management (HLM) specification announcement.
 
Article
Research on wireless sensor networks (WSNs) has received tremendous attention in the past few years due to their potential applications and advances in the VLSI design. In WSNs with tiny sensors, mobility of a sink may provide an energy efficient way for data dissemination. Having a mobile sink in WSN, however, creates new challenges to routing and sensor distribution modeling in the network. In this paper, based on clustering and routing optimization algorithms, we propose a new scheme called K-means and TSP-based mobility (KAT mobility). After clustering the sensor nodes, the proposed method navigates the mobile sink to traverse through the cluster centers according to the trajectory of an optimized route. The mobile sink then collects the data from sensors at the visited clusters. Simulation results have demonstrated that the proposed scheme can provide not only better energy efficiency as compared to those obtained by conventional methods which assume random waypoint for the mobile sink, but also fault-resilience in case of malfunctions of some sensors due to attacks.
 
Article
We address the challenges of bursty convergecast in multi-hop wireless sensor networks, where a large burst of packets from different locations needs to be transported reliably and in real-time to a base station. Via experiments on a 49 MICA2 mote sensor network using a realistic traffic trace, we determine the primary issues in bursty convergecast, and accordingly design a protocol, RBC (for Reliable Bursty Convergecast), to address these issues: To improve channel utilization and to reduce ack-loss, we design a window-less block acknowledgment scheme that guarantees continuous packet forwarding and replicates the acknowledgment for a packet; to alleviate retransmission-incurred channel contention, we introduce differentiated contention control. Moreover, we design mechanisms to handle varying ack-delay and to reduce delay in timer-based retransmissions. We evaluate RBC, again via experiments, and show that compared to a commonly used implicit-ack scheme, RBC doubles packet delivery ratio and reduces end-to-end delay by an order of magnitude, as a result of which RBC achieves a close-to-optimal goodput.
 
Article
The Wireless World Research Forum (WWRF) is a global academic and industry forum, which is contributing to the visions of future wireless communications and is identifying research topics on which to build the vision. The next two decades promises us almost unimaginable communication capabilities; the technology can deliver almost anything we want it to, but the key to success is understanding what capabilities people will find valuable, and how to simply access those capabilities. The WWRF is putting the user at the centre of its visions by identifying research, which uncovers the functionality that people will value in the future. These research topics fall into three areas; understanding the user, by studying human behaviour and needs, the development of next generation technologies becomes user requirements driven rather than technology lead; new generic application elements, in which technologies closely associated with the understanding of the user, such as virtual reality, are identified for research; and new interaction techniques, which allow for intuitive interaction between humans and the terminals and underlying network services. Studying the user, especially in these research areas, is the only way to ensure that the future wireless world meets and exceeds the expectations of people in the coming decades.
 
Article
We provide an example to illustrate the worst case message complexity of two of heuristics (R. Sriram, G. Manimaran, C.Siva Ram Murthy, Preferred link based delay-constrained least cost routing in wide area networks, Computer Communiations, 21(1998), 1655–1669) is exponential which was not stated by the authors.
 
Article
Embedding a Radio Frequency Identification (RFID) tag into individual items enables the unique identification of such items over the wireless medium, without the need for a line-of-sight path. One of the main challenges for the successful commercialization of the RFID technology is the efficient, yet private, identification of low-cost tags in the presence of adversaries attempting to illegally track users via tags in their possession. An RFID system consists of two functional components, namely, the interactive protocol between RFID reader-tag pairs and the reader-database information retrieval mechanism. Because of the large number of tags in a typical RFID system, the private identification of tags can be a challenging problem. In this paper, we investigate privacy-preserving RFID systems and classify them based on the computational efficiency of tag identification. We show the close relation between the degree of privacy achieved by the reader-tag interaction and the reader-database information retrieval complexity.
 
Article
An evaluation of the 1984 and 1988 CCITT X.400 series of recommendations is given with particular reference to the use of a Message Handling System (MHS) for interpersonal communication. The human user's needs in electronic communication are studied. Based on these findings, the technical quality of the services provided are evaluated, as is the support of the human factors in communication. MHS is evaluated in terms of its suitability for the individual user and the applicability for communication in groups. Message handling services are presented and compared with user requirements. In particular, the new services of the X.400 recommendations of 1988 concerning interworking with Directory Services (DS), the security model, message store and distribution lists are examined to determine how they meet the needs of the human user, and how they could be used or extended to improve communication in groups.
 
Article
As cellular networks are evolving into high data rate systems, cdma2000 1x EV-DO (HDR) has been highlighted and deployed for data-only wireless service. For wide applications, it is expected to serve some real-time traffic including VoIP. To meet the loss requirement and to ensure the delay bound of VoIP packets, we consider two scheduling algorithms that are channel-aware and flexible in the frame structure; maximal rate (MAX) algorithm and proportionally fair (PF) algorithm. The PF algorithm was known to be appropriate for elastic traffic, not real time traffic. However, through simulations, we find that the PF algorithm with a simple channel test can become a good approach for supporting VoIP users. When the required slot portion of VoIP is 75%, this algorithm obtains the loss rate of about 1% on the average and 3% in the worse case. On the other hand, the MAX algorithm shows twice of the loss rate when the same delay bound and load are given. These results provide an insight in designing a simple admission control scheme for VoIP users to control the average portion of slots occupied by VoIP packets.
 
Article
Key aspects in realizing the maximum potential of advanced Location-Based Services (LBS) are the standardization and cross-platform availability of an Application Programming Interface (API) for mobile phones that allows access to real-time location information. To shorten the development time of advanced LBS, such an API should also provide essential features such as map user interfaces, geocoding, and navigation to be used as building blocks in the context of larger mobile applications. Using these available services, application developers can focus on building innovative location-aware applications rather than re-creating existing services. This article’s main goals are to emphasize the importance of such an API and to describe the Location API for Java 2 Micro Edition (J2ME). This description includes the main features of the current “JSR179-Location API v1.0” as well as the significant enhancements and new services included in the development of “JSR293-Location API v2.0.” These new features, illustrated using coding examples, will help software developers create next-generation location-aware J2ME applications.
 
Article
This manuscript is a contribution on the modeling of H.263 traffic in multipoint videoconference sessions over IP Networks. Our study includes analysis and modeling assessment of extensive data gathered during realistic videoconference sessions between commercial H.263-compliant terminal clients (with different videoconference software packages installed). All terminal clients were communicating through a Multipoint Control Unit (software or hardware MCU) at ‘switched presence’ mode and for comparative purposes the same typical videoconference content (a person speaking, with mild movement and occasional zoom/span) was used. The analysis of the H.263 data at the frame level suggests that the traffic from the different terminals to the MCU can be represented by a stationary stochastic process with an AutoCorrelation Function (ACF) rapidly decaying to zero and a Gamma formed marginal frame-size Probability Distribution Function (PDF). An accurate analysis of the H.263 traffic from all terminals (with the same visual content and different videoconference software used) shows indicative differences in the ACF and PDF of different terminals' traffic and insights that no generic traffic model can be applied for all cases. Aiming at a realistic, reusable and simple H.263 traffic model, conservative enough for queueing analysis and network estimation, this study discusses methods for calculating the appropriate model parameters from the observed traffic data and proposes a new technique for unconventional fitting of the PDF. The presented modeling and queueing results indicate the suitability of the proposed models for H.263 traffic modeling in IP networks. http://www.sciencedirect.com/science/article/pii/S0140366405001180
 
Article
Efficient H.264 video transmission over wireless/mobile networks becomes dominant, because H.264 is adopted as a dominant video coding standard in mobile broadcasting and in other advanced video streaming. However, wireless video transmission suffers from poor wireless channel conditions, such as high bit error rate and error bursts resulting from channel fading and radio interference. In this paper, a novel design of unified error-control with cross-layer interactions over IEEE 802.11e wireless LAN and an efficient low-overhead ARQ scheme are proposed. This framework combines cross-layer error protection techniques composed of error correction code in the link/MAC layer, erasure code in the application layer, and ARQ across the link/MAC layer and application layer. In this framework, a guideline for quality improvement of the cross-layer approach is also developed and offered. In addition to the unified cross-layer error-control framework, an efficient MAC-level ARQ scheme with low-overhead is also proposed. The several cases of low-overhead ARQ scheme combined with or without cross-layer interaction are compared and discussed for performance evaluation.
 
Article
In this correspondence, we initially investigate the statistical behavior of bursty video traffic originating from single H.264/AVC streams, by modeling it with well-known distributions. Our results help to build a Discrete Autoregressive model which captures well the behavior of multiplexed H.264/AVC videoconference sources.
 
Article
In wireless cellular networks, location management operation expends the limited wireless resources to keep track the location information of a mobile terminal. Various dynamic location update (LU) schemes have been proposed to improve the efficiency of location management. However, most of them only work for certain mobility patterns. In this paper, we propose a new scheme that the LU area is adaptively designed according to the mobility pattern and traffic parameters. The 2D Markov walk is used as the mobility model which describes a broad class of mobility patterns. A recursive algorithm is developed to compute the location management cost of a general LU area shape. Due to the high computational complexity of the adaptive LU area design problem, we use an iterative greedy heuristic algorithm to find an approximation solution of the problem efficiently. The effects of the mobility patterns and traffic parameters on the designed LU area shape are investigated. Experimental results show that the LU area designed by the heuristic algorithm can adaptively change according to the given mobility pattern and traffic parameters. Compared with some existing dynamic LU schemes, the proposed adaptive LU scheme is more flexible and efficient for location management.
 
Article
In hierarchical sensor networks, sensor nodes are arranged in clusters, and higher-powered relay nodes can be used as cluster heads. Due to the limited transmission range and battery power of the nodes, it is important to develop techniques that minimize energy dissipation of the nodes, and thus extend the lifetime of network. Proper techniques for assigning sensor nodes to clusters have been shown to improve the lifetime of the network. In this paper, we have proposed two fast and efficient integer linear program (ILP) formulations for assigning sensor nodes to clusters in a two-tiered network, where the relay nodes are used as cluster heads. The first is for single hop routing and the second is a generalized formulation that can be used with any multi-hop routing strategy. The objective, in both cases, is to maximize the lifetime of the relay node network. Comparisons with existing heuristics for clustering demonstrate that our ILP’s significantly extend the network lifetime and are fast enough to be used for practical networks with hundreds of sensor nodes.
 
Article
This paper discusses the scalability problem of distributed virtual environment (DVE) centered on area of interest (AOI) model and dead reckoning (DR) algorithm. Previous models improving scalability of virtual environment are analyzed and compared, and a new adaptive message-filtering algorithm based on DR is proposed. The proposed model can be utilized for distributed interactive simulation (DIS) and various network applications such as multi-player games and virtual communities. The most distinguished characteristic of the proposed model is the introduction of flexible threshold mechanism (FTM). It is inefficient that in static dead reckoning (SDR) algorithm, moving avatar straightly and frequently rotating one are uniformly considered. The proposed model overcomes the weak point of established DR caused by a fixed threshold and a strong dependency on rotational behavior of moving avatars. This paper defines a new criterion for update message filtering, named as update lifetime (UL), which is a valid duration time of entity state update. The advantage of dynamic approaches proposed in this paper is the ability of keeping the balance between fidelity and performance in filtering. In experimental results, it was shown that intelligent DR lowered the increment rate of update message traffic over the increase of behavioral complexity of avatar without any significant loss of accuracy.
 
Article
Next generation of wireless cellular networks aim at supporting a diverse range of multimedia services to mobile users with guaranteed quality of service (QoS). Resource allocation and call admission control (CAC) are key management functions in future 3G and 4G cellular networks, in order to provide multimedia applications to mobile users with QoS guarantees and efficient resource utilization. There are two main strategies for radio resource allocations in cellular wireless networks known as complete partitioning (CP) and complete sharing (CS). In this paper, theses strategies are extended for operation in 3G and beyond network. First, two CS-based call admission controls, referred to herein as queuing priority call admission control (QP-CAC) and hybrid priority call admission control (HP-CAC), and one CP-based call admission control referred to as complete partitioning call admission control (CP-CAC) are presented. Then, this study proposes a novel dynamic procedure, referred to as the dynamic prioritized uplink call admission control (DP-CAC) designed to overcome the shortcomings of CS and CP-based CACs. Results indicate the superiority of DP-CAC as it is able to achieve a better balance between system utilization, revenue, and quality of service provisioning. CS-based algorithms achieve the best system utilization and revenue at the expense of serious unfairness for the traffic classes with diverse QoS requirements. DP-CAC manages to attain equal system utilization and revenue to CS-based algorithms without the drawbacks in terms of fairness and service differentiation.
 
Article
In current and next 3G and beyond wideband code-division with multiple access (WCDMA) cellular networks, sharing the radio access network has become an important issue for 3G mobile operators. 3G and beyond network rollout is a very costly and time consuming process. Therefore, sharing of network infrastructure among operators offers an alternative solution to reducing the investment in the coverage phase of WCDMA. In radio access network (RAN) sharing method, which is our focus in this study, each operator has its own core network and only the RAN is shared. It implies that multiple operators fully share the same RAN. Without an efficient RRM, one operator can exhausts the capacity of others. This study tackles an efficient scheduling to provide maximum system throughput and proportional fairness in accordance with operator capacity share through adaptive resource allocation scheme. We refer to this new scheme as Multi-operators Code Division Generalized Processor sharing scheme (M-CDGPS). It employs both adaptive rate allocation to maximize the resource utilization and GPS techniques to provide fair services for each operator. The performance analysis in terms of bounded delay and queue size are obtained.
 
Article
Although, many architectures (Integrated Services, Differentiated Services, MPLS, Traffic Engineering, etc.) have been proposed to provide service differentiation in fixed networks, research has shown that what works well in a wired network cannot be directly applied in the wireless environment where bandwidth is scarce and channel conditions are time varying. Quality of Service (QoS) is a key challenge for today's wireless IP networks and implementation of QoS, particularly for supporting voice, video, data and multimedia services in general incurs a number of difficulties that have to be analysed and resolved. A considerable amount of work has been carried out by the various standards groups in an effort to quantify and specify protocols to support QoS in wireless environments. This paper reports on these efforts outlining existing limitations, requirements and solutions proposed by organisations such as the IEEE 802.11 Task Group E for wireless LANs and the UMTS effort for 3G/wireless WANs.
 
Article
The seamless continuity of services between 3G networks and WLANs will give users the feeling of a common environment towards the wireless technology. Three main aspects must be considered to obtain seamless continuity: an enabling interworking architecture, fast inter-system handovers (they must be fast enough in terms of human senses), and, in the case of real-time services, a similar quality of service (QoS) in both networks. This paper focuses on the two first issues. It presents an interworking architecture based on a 3G core-level integration of the WLANs. The GPRS network is available all the time forming a primary network, and WLANs are used as a complement when they are available. The switching times between networks are very low and the transitions are lossless. Our proposal does not disrupt with the current 3GPP standardization efforts making it viable in a medium time frame. This paper presents an overview of the architecture, describes the relevant events in the switching process (where the authentication and authorization procedures have an important role), and gives simulated values for the switching times.
 
Article
Orthogonal variable spreading factor (OVSF) codes are employed as channelization codes in wideband CDMA. Any two OVSF codes are orthogonal if and only if one of them is not a parent code of the other. Therefore, when an OVSF code is assigned, it blocks all of its ancestor and descendant codes from assignment because they are not orthogonal to each other. Unfortunately, this code-blocking problem of OVSF codes can cause a substantial spectral efficiency loss of up to 25%. This paper presents non-blocking OVSF (NOVSF) codes to increase substantially the utilization of channelization codes without having the overhead of code reassignments. In addition, an encoding algorithm is presented to increase network capacity and support higher data rates when NOVSF codes are employed.
 
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Most of the currently available adaptation solutions of VoIP over UMTS are based on the modification of service parameters as the only available reaction against any detected service degradation. On the contrary, in this paper we propose a combined approach where service-level adaptation is considered first and, provided that no suitable parameter combination is capable of providing enough QoE, a change of network state will be suggested. In order to do so we analyze the performance of the end-to-end (e2e) performance metrics in this convergent scenario, the root causes of possible degradations and, finally, the combined effects of the different network segments and their impact on the user perceived QoE. We show the map of best performing VoIP configurations for every state of the network segments. Furthermore, considering each of these configurations, we analyze the acceptability of the service or the convenience of trying to modify the network state. Finally, a lightweight implementation based on simple network state estimation and decision heuristics is proposed and validated in terms of accuracy and responsiveness.
 
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Recently, sharing the radio access network (RAN) has become an important issue for 3G and beyond mobile wireless operators. In addition to user and service considerations, there are economic and technical advantages to 3G and beyond shared networks. This is driving optimizations in the deployment and development of national 3G and 4G rollouts. However, shared 3G and 4G networks exhibit many of the resource management opportunities and challenges as more complex heterogeneous traffic and sharing techniques are considered.In this paper, we propose a roaming-based sharing adaptive partitioning with borrowing (APB) scheme where an operator is allowed to borrow from the unutilized resources originally belonging to other operators sharing the same RAN. This algorithm controls the resource sharing between the operators in addition to controlling the admission control (CAC) within each operator’s domain. The borrowing margin is specified either as a fixed portion or an adaptive percentage of the unutilized resource. Furthermore, the APB CAC function makes a distinction between newly originating calls and handoff calls by assuming a higher priority level for handoff calls in the form of possibility of queuing. Therefore, the prescribed call admission control scheme provides a higher quality of service for the handoff requests of real-time services expected in 3rd and 4th G wide band code division multiple access (WCDMA) systems. Simulation results indicate that APB provides higher resource utilization under all load conditions leading in turn to increased revenue. In addition, a higher quality of service for traffic is provided especially when an operator is allowed to borrow from the unutilized resources.
 
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Multicast can greatly save network bandwidth because only one copy of data is transmitted in the shared paths. Applications such as video conferences and network games usually can benefit from multicast. Although mobile multicast has been studied for years, it is still a challenge and has not been widely realized in today’s Internet. Both 3GPP and 3GPP2 have defined architectures and protocols for multicast. This paper presents the multicast architectures and operations defined in 3GPP and 3GPP2. Besides, this paper also provides a systematic comparison of them. In addition to system architectures, various issues including mobility, QoS, and security are discussed. Moreover, we discuss the challenges in radio resource management (RRM), power control, scalability, and complexity. This paper could be a reference for those seeking the perspective often difficult to obtain from standards specifications.
 
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This paper presents an efficient link-sharing method for available bit rate and unspecified bit rate services in ATM networks. The method comprises an algorithm that performs cell multiplexing and scheduling such that the outgoing link is fairly shared by multiple traffic flows. The proposed algorithm adopts a dynamic priority assignment to each ATM cell, and schedules those cells having the same priority level into repeating cycles in a round-robin fashion. The algorithm also guarantees each ABR connection a specified minimum cell rate and a satisfied cell loss rate. The performance is evaluated through simulations and is also compared with another fixed method called weighted round robin. Finally, a corresponding hardware design that uses a two-stage leaky bucket circuit is presented.
 
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Network operators, service providers and customers are players who have different interests and raise different requirements on the functionality of future mobile communication networks. However, some new capabilities, such as mobility, security, ubiquity and quality are spelled out by all, which means that there exist some fundamental mechanisms which are in fact needed in every network. This paper concentrates on critical elements of the network infrastructure which need to be deployed in 4G networks before services can be offered. In the paper we discuss these elements, and show how they can be combined to satisfy versatile service requirements. Furthermore, the paper shows how to combine these mechanisms of three traditionally quite separate architectures-for Authentication, Authorisation, Accounting and Charging (AAAC), for Mobility (Mobile IP with Fast Handover), and Quality-of-Service (QoS). A technology-independent paging concept is also integrated in this system. The resulting integrated system architecture is general and can be deployed in heterogeneous environments. Our implementation has recently been completed, validated and verified with applications such as data transfer, voice-over-IP, video streaming and real time concurrent gaming. This prototypical implementation incorporates TD-CDMA, 802.11 WLANs and Ethernet, and treats all transmission technologies as physical and data-link layers, while higher-level functions are supported in a uniform way with an all-IPv6-based signalling.
 
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Providing seamless mobility support is one of the most challenging problems towards the system integration of fourth generation (4G) wireless networks. Because of the transparency to the lower layer characteristics, application-layer mobility management protocol like the Session Initiation Protocol (SIP) has been considered as the right candidate for handling mobility in the heterogeneous 4G wireless networks. SIP is capable of providing support for not only terminal mobility but also for session mobility, personal mobility and service mobility. However, the performance of SIP, operating at the highest layer of the protocol stack, is only as good as the performance of the underlying transport layers in such a heterogeneous environment. In this paper we analyze the handoff performance of SIP in a IP-based 4G network with Universal Mobile Telecommunication System (UMTS) and Wireless LAN (WLAN) access networks. Analytical results show that the handoff to a UMTS access network introduces a minimum delay of 1.4048 s for 128 kbps channel, while for handoff to a WLAN access network the minimum delay is 0.2 ms. In the former case the minimum delay is unacceptable for streaming multimedia traffic and requires the deployment of soft-handoff techniques in order to reduce the handoff delay to a desirable maximum limit of 100 ms.
 
Top-cited authors
J.M. Rabaey
  • University of California, Berkeley
Shad Roundy
  • University of Utah
Mohamed Younis
  • University of Maryland, Baltimore County
Stefano Chessa
  • Università di Pisa
Yim Fun Hu
  • University of Bradford