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Non-ideal channel conditions degrade the performance of wireless networks due to the occurrence of frame errors. Most of the well-known works compute the saturation throughput and packet delay for the IEEE 802.11 Distributed Coordination Function (DCF) protocol with the assumption that transmission is carried out via an ideal channel (i.e., no channel bit errors or hidden stations), and/or the errors exist only in data packets. Besides, there are no considerations for transmission errors in the control frames (i.e., Request to Send (RTS), Clear to Send (CTS), and Acknowledgement (ACK)). Considering the transmission errors in the control frames adds complexity to the existing analysis for the wireless networks. In this paper, an analytical model to evaluate the Medium Access Control (MAC) layer saturation throughput and packet delay of the IEEE 802.11g and IEEE 802.11n protocols in the presence of both collisions and transmission errors in a non-ideal wireless channel is provided. The derived analytical expressions reveal that the saturation throughput and packet delay are affected by the network size (n), packet size, minimum backoff window size (Wmin), maximum backoff stage (m), and bit error rate (BER). These results are important for protocol optimization and network planning in wireless networks. [ABSTRACT FROM AUTHOR]

The paper presents a new steganographic method called RSTEG (retransmission steganography), which is intended for a broad class of protocols that utilises retransmission mechanisms. The main innovation of RSTEG is to not acknowledge a successfully received packet in order to intentionally invoke retransmission. The retransmitted packet carries a steganogram instead of user data in the payload field. RSTEG is presented in the broad context of network steganography, and the utilisation of RSTEG for TCP (transmission control protocol) retransmission mechanisms is described in detail. Simulation results are also presented with the main aim of measuring and comparing the steganographic bandwidth of the proposed method for different TCP retransmission mechanisms, as well as to determine the influence of RSTEG on the network retransmission level. [ABSTRACT FROM AUTHOR]

High data rate wireless technologies are now becoming a reality, and have spurred the development of new applications that were previously hindered by the lack of capacity. In particular, it is now possible to stream high definition movies from a laptop to a sound system and flat screen television seamlessly. One of the key enablers of such applications is the IEEE 802.15.3 medium access control (MAC) protocol, which is designed to support bandwidth intensive applications in wireless personal area networks (WPANs). A key observation is that a significant number of multi-media applications rely on the transmission control protocol (TCP). Unfortunately, little works have conducted a thorough performance study of TCP over the IEEE 802.15.3 MAC. Moreover, the IEEE 802.15.3 specification does not specify any strategies for allocating time slots. This paper therefore contributes to the current state-of-the-art in the following manners. From our extensive analytical and simulation studies, we reveal the impacts of different channel time allocation methods and acknowledgment policies on the performance of TCP, with particular attention on round trip time, congestion window growth, and packet recovery. We then present the following guidance to application developers: (1) channel time allocations (CTAs) should be distributed evenly over the superframe and have durations determined by TCP’s maximum congestion window, (2) CTA positioning has no impact on TCP’s performance, and (3) the specified delayed acknowledgment policy needs to be augmented with an adaptive algorithm that adjusts its burst size dynamically to varying bit error rate (BER). [ABSTRACT FROM AUTHOR]

In time-critical wireless sensor network (WSN) applications, a high degree of reliability is commonly required. A dynamical jumping real-time fault-tolerant routing protocol (DMRF) is proposed in this paper. Each node utilizes the remaining transmission time of the data packets and the state of the forwarding candidate node set to dynamically choose the next hop. Once node failure, network congestion or void region occurs, the transmission mode will switch to jumping transmission mode, which can reduce the transmission time delay, guaranteeing the data packets to be sent to the destination node within the specified time limit. By using feedback mechanism, each node dynamically adjusts the jumping probabilities to increase the ratio of successful transmission. Simulation results show that DMRF can not only efficiently reduce the effects of failure nodes, congestion and void region, but also yield higher ratio of successful transmission, smaller transmission delay and reduced number of control packets. [ABSTRACT FROM AUTHOR]

An energy-efficient adaptive transmission protocol for ultrawideband (UWB) wireless sensor networks (WSNs), called ATP-UWSN, is described and evaluated over time-varying multipath fading channel conditions and multinode interference. Since wireless channels may greatly change from one transmission to the next, the use of fixed transmission parameters for such channels results in wasted energy when channel conditions are good. Adaptation of transmission parameters reduces energy consumption and interference. The proposed ATP-UWSN permits each of the sensor nodes to adapt its code rate and spreading code length (the number of pulses used per data bit) to match the predicted channel-state information (CSI). The transmission parameters are selected in accordance with the predicted CSI characteristics of the communication links in the network to achieve the desired quality of service given by the target bit-error probability. Subsequently, we develop a mathematical adaptation framework for the analytical evaluation of ATP-UWSN. Communication performance is evaluated in terms of average information throughput efficiency, which is a relevant progress-related measure for multihop WSNs that is associated with the energy consumption and throughput of a packet transmission. The analytical expression of this performance metric is defined and is used to assess the benefits of the proposed ATP-UWSN when compared with a nonadaptive transmission protocol (NATP) with fixed transmission parameters. Our results show that the ATP-UWSN outperforms the NATP and can improve the robustness of the link and reduce energy consumption by adapting the transmission parameters in response to changes in the predicted CSI. [ABSTRACT FROM AUTHOR]

Growing numbers of service providers are implementing video services over IP networks, and discovering the unique challenges of providing a high quality-of-experience (QoE) to subscribers. Delivering consistent QoE in packet-switched networks can be a complex proposition due to the high sensitivity of video traffic to packet loss, as well as to delay and jitter. Preserving video quality in IP Television (IPTV) networks that mostly rely on copper access lines poses an even greater challenge. Service providers need intelligent mechanisms in core and distribution networks to prevent congestion that deteriorates video quality, as well as intelligence between the aggregation networks and IP set-top box (STB) to repair packet losses, speed up channel change times and monitor the quality of the subscriber experience. This paper discusses a series of core and aggregation-layer approaches, collectively referred to as Visual Quality of Experience (VQE) to address these issues. The VQE approach encompasses on-path video connection admission control (CAC) employing Resource ReSerVation Protocol (RSVP) in the core and aggregation layers, and a real-time signaling mechanism operating between the provider aggregation edge and the IP STBs to address packet losses, long channel change times and quality monitoring. [ABSTRACT FROM AUTHOR]

The advent of IP/MPLS based networks allows providers to implement Integrated Services Packet Network (ISPN) concepts for IPTV applications. IPTV systems require a high level of Quality of Service (QoS) in order to win customers which are subscribed with cable companies. Packet loss probability is one of the primary QoS parameters whose value affects the user experience and which provides a quantitative measure for customers' perception of the QoS factor in practical networks. Therefore, the online accurate measurement and estimation of the packet loss probability is a key issue to be addressed. Furthermore, the packet loss probability provides the feedback information which can be used in the network based control system to maintain it at a prescribed and negotiated value. In this paper, a Reactive Estimator (RE) of the packet loss probability is constructed. As all parameters related to the network traffic, the packet loss is a non-linear and non-Gaussian stochastic process. The proposed RE has the capability to adapt to variable stochastic contexts by employing one dynamic item based on the feedback of the real-time loss ratio measurement. A series of experiments are devised on a live network to evaluate the performance of the estimator under multiple traffic arrival models and within various buffer sizes. The numeric results show that the practical estimator is accurate enough to approximate the packet loss probability, such that it can be further used as a feedback parameter in a closed control loop which can keep the packet loss probability close to a prescribed value. [ABSTRACT FROM AUTHOR]

Internet Protocol TV (IPTV), an emerging internet application, provides more flexibility and interactivity for users because of its embedded return channel. Wireless 802.11 networks, used as the last hop of IPTV networks, would add another dimension of mobility, which is of great value for hot spot deployment and is increasingly required for in-home content distribution. However, a wireless channel may suffer from multi-path fading and interference, which may cause random and burst packet loss and impact users' quality of experience of an IPTV program. We report the design, implementation and evaluation of Merged Hybrid Adaptive FEC and ARQ (MHARQ) system for IPTV multicast over wireless LANs. In MHARQ, an IPTV cache server is introduced to improve the reliability for the last hop wireless distribution. MHARQ combines the advantages of receiver-driven staggered FEC and hybrid ARQ schemes to compensate the large dynamic range of WLAN channels and to achieve high reliability, scalability and wireless bandwidth efficiency for IPTV multicast. We also address backward compatible FEC encoding and decoding, audio and video synchronization issues in practical system implementation. Using the ORBIT radio grid test bed, we have investigated the performance of the proposed MHARQ system with various numbers of users per AP and different numbers of APs per IPTV cache server. It is demonstrated via real system implementation on ORBIT that MHARQ improves wireless bandwidth efficiency and scalability for reliable IPTV multicast, compared with existing reliable multicast schemes. [ABSTRACT FROM AUTHOR]

Interference is a serious problem in wireless communications. In a wireless network, the signal sent by a terminal will be received by all its neighboring nodes. If a neighbor (except the destinations) is receiving data from some other terminals at the same time, the signals will collide, and the useful signal will be destroyed, which may result in transmission failure. Previous solutions to this problem focused on the avoidance of signal collisions through careful medium access control (MAC) and/or scheduling. However, this needs some sophisticated protocols and may waste system resources such as bandwidth. In this paper, we shall put forward some practical schemes to recover the useful signal from the collided signals for different types of wireless channels; thus, the throughput and network efficiency can greatly be increased. The proposed schemes are based on the network coding technique and performed on the physical layer. One feature of our schemes is that neither strict synchronization nor power control is needed among the different terminals; thus, it is very fit for distributed networks. Simulation results will show that the bit error rate (BER) of the recovered signal by our developed schemes is almost the same as that of the signal with no collision, which proves their efficiency in eliminating the interference. [ABSTRACT FROM AUTHOR]

This article investigates distributed cooperative medium access control protocol design for multihop wireless networks. Cooperative communication has been proposed recently as an effective way to mitigate channel impairments. With cooperation, single-antenna mobile terminals in a multi-user environment share antennas from other mobiles to generate a virtual multiple-antenna system that achieves more reliable communication with a higher diversity gain. However, more mobiles conscribed for one communication inevitably induces complex medium access interactions, especially in multihop wireless ad hoc networks. To improve the network throughput and diversity gain simultaneously, we investigate the issues and challenges in designing an efficient MAC scheme for such networks. Furthermore, based on the IEEE 802.11 DCF, a cross-layer designed cooperative MAC protocol is proposed. The MAC scheme adapts to the channel condition and payload length. [ABSTRACT FROM AUTHOR]

Recent studies demonstrated that dynamic spectrum access can improve spectrum utilization significantly by allowing secondary unlicensed users to dynamically share the spectrum that is not used by the primary licensed users. Cognitive radio was proposed to promote the spectrum utilization by opportunistically exploiting the existence of spectrum "holes." Meanwhile, cooperative relay technology is regarded widely as a key technology for increasing transmission diversity gain in various types of wireless networks, including cognitive radio networks. In this article, we first give a brief overview of the envisioned applications of: cooperative relay technology to CRNs, cooperative transmission of primary traffic by secondary users, cooperative transmission between secondary nodes to improve spatial diversity, and cooperative relay between secondary nodes to improve spectrum diversity. As the latter is a new direction, in this article we focus on this scenario and investigate a simple wireless network, where a spectrum-rich node is selected as the relay node to improve the performance between the source and the destination. With the introduction of cooperative relay, many unique problems should be considered, especially the issue for relay selection and spectrum allocation. To demonstrate the feasibility and performance of cooperative relay for cognitive radio, a new MAC protocol was proposed and implemented in a universal software radio peripheral-based testbed. Experimental results show that the throughput of the whole system is greatly increased by exploiting the benefit of cooperative relay. [ABSTRACT FROM AUTHOR]

In this paper, we consider the binary-distributed hypothesis testing problem, where a wireless sensor network (WSN) is used to determine the true state of nature. We propose a novel signaling scheme where signature vectors (SVs) are used to transmit censored sensor decisions to the fusion center (FC). In particular, the length of the SVs is chosen to be smaller than the number of sensors, resulting in nonorthogonal sensor channels and allowing a desirable tradeoff between bandwidth and power efficiency in WSNs. We consider deterministic SVs that are assumed to be known to the FC and random SVs that are unknown to the FC. For both cases, the optimum noncoherent fusion rules are derived, assuming independent Ricean fading sensor-FC channels. Since the complexity of these optimum fusion rules is prohibitively large, even for WSNs of moderate size, we also consider a low-complexity suboptimum energy-based fusion rule and show that it is equivalent to the optimum fusion rules under certain conditions. Furthermore, we calculate the system probabilities of detection and false alarm for the energy-based fusion rule for both deterministic and random SVs. Numerical and simulation results show that with the proposed nonorthogonal signaling scheme, significant improvements in bandwidth efficiency are possible at the expense of only a small loss in power efficiency. [ABSTRACT FROM AUTHOR]

The paper presents a detailed discussion of various issues involved in designing a medium access control (MAC) protocol for multihop wireless networks with nodes employing multiple beam smart antennas. Multiple beam smart antennas can form several beams simultaneously and can initiate concurrent transmissions or receptions in them, thereby increasing the throughput of the bottleneck nodes. Traditional on-demand MAC protocols for omnidirectional and single beam directional antennas based on the IEEE 802.11 distributed coordination function (DCF) mechanism cannot take advantage of this unique capability of multiple beam antennas as they do not facilitate concurrent transmissions or receptions by a node. This paper introduces a novel protocol, hybrid MAC .(HMAC), which enables concurrent packet reception (CPR) and concurrent packet transmission (CPT) at a node equipped with multiple beam antennas and is backward compatible with IEEE 802.11 DCF. Simulation results show the superior performance of HMAC in most ad hoc scenarios. Moreover, in some sample topologies, the throughput of HMAC is close to the theoretical maximum. The paper also presents a wireless mesh network architecture with heterogeneous antenna technologies and illustrates the advantages of employing multiple beam smart antennas and HMAC in such networks. [ABSTRACT FROM AUTHOR]

We investigate the behaviour of TCP(α, β) protocols in the presence of wireless networks. We seek an answer to strategic issues of maximizing energy and bandwidth exploitation, without damaging the dynamics of multiple-flow equilibrium. We take a fresh perspective on protocol design: What is the return of the effort that a protocol expends? Can we achieve more gains with less effort? We study first the design assumptions of TCP(α, β) protocols and discuss the impact of equation-based modulation of α and β on protocol efficiency. We introduce two new measures to capture protocol behaviour: the ‘Extra Energy Expenditure’ and the ‘Unexploited Available Resource Index’. We confirm experimentally that, in general, smoothness and responsiveness constitute a tradeoff; however, we show that this tradeoff does not graft its dynamics into a conservative/aggressive behaviour, as it is traditionally believed. We uncover patterns of unjustified tactics; our results suggest that an adaptive congestion control algorithm is needed to integrate the dynamics of heterogeneous networks into protocol behaviour. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Previous application sharing systems have no unified communication protocols. The well known application sharing protocols include RFB (Remote FrameBuffer), RDP (Remote Desktop Protocol) and ITU-T T.128. A generic application sharing architecture is proposed for providing the capability of connecting various application sharing servers with the same application sharing client. A communication standard for application sharing systems is defined based on the Message-Oriented Middleware (MOM). To compare with previous application sharing systems, there are many advantages including easy to use, easy to connect, easy to integrate, higher scalability and less bandwidth consumption. [Copyright &y& Elsevier]

In the last decade, process instrumentation field devices such as sensors and actuators that have a direct contact with industrial processes have become increasingly intelligent. An important property of such intelligent field devices is their ability to be networked. The Foundation fieldbus (FF) is one of the most widely used fieldbus protocols for process instrumentation and control systems applications. This paper presents a study that validates the effectiveness of a new scheduling method that satisfies the performance requirements for a scheduled message using an FF protocol. Our scheduling method generates a schedule list that records the scheduled starting time and the scheduled period of each scheduled message. Then, it allocates scheduled message traffic to a bandwidth-limited fieldbus medium. As part of this study, an experimental model of an FF network was developed. The experimental results from our model confirmed that our scheduling method restricts the delay of a scheduled message to a prespecified bound. [ABSTRACT FROM AUTHOR]

A new on-wafer noise parameter measurement method at a 2.8-18-GHz frequency band is presented. This measurement method is based on both temporal and spectral analysis of noise power measurements. We present the method and the experimental results on an active two-port. It requires less equipment than the classic noise parameter measurement method. It gives direct results for 801 points in the 2.8-18-GHz frequency band. [ABSTRACT FROM AUTHOR]

As communications networks become increasingly dynamic, heterogeneous, less reliable, and larger in scale, it becomes difficult, if not impossible, to effectively manage these networks using traditional approaches that rely on human monitoring and intervention to ensure they operate within desired bounds. Researchers and practitioners are pursuing the vision of autonomic network management, which we view as the capability of network entities to self-govern their behavior within the constraints of business goals that the network as a whole seeks to achieve. However, applying autonomic principles to network management is challenging for a number of reasons, including: • A means is required to enable business rules to determine the set of resources and/or services to be provided. • Contextual changes in the network must be sensed and interpreted, because new management policies may be required when context changes. • As context changes, it may be necessary to adapt the management control loops that are used to ensure that system functionality adapts to meet changing user requirements, business goals, and environmental conditions. • A means is required to verify modeled data and to add new data dynamically so that the system can learn and reason about itself and its environment. This article provides an introduction to the FOCALE autonomic network management architecture, which is designed to address these challenges. [ABSTRACT FROM AUTHOR]

Giving the operator the ability to manage in-home devices greatly increases the potential of the cost-efficient provision of new profitable services. In this spirit, standardization undertaken by the DSL forum not only addresses remote management of the residential gateway but recently, also extends to in-house devices. We propose a solution that bridges remote management specified by CWMP with UPnP, already established inside the home environment. This approach will enable providers to remotely configure and manage in-house UPnP-enabled equipment, thus accelerating the deployment of new services. We investigate the nature of the two protocols and specify the bridging functionality, taking into consideration scalability and transparency. Experimental results support the applicability of the proposed approach, highlight the importance of message filtering, and provide general insight into the interplay intricacies of the particular protocol functions. [ABSTRACT FROM AUTHOR]

The home gateway market is undergoing deep changes. On one side, home networks are evolving, getting dynamic and federating more and more devices. On the WAN side, new actors appear, such as multimedia content providers. From both sides emerge new features and new management needs. In this article we highlight challenges and benefits of moving more intelligence to the home gateway, making it more than a simple interconnection device. We argue that we need a full-fledged execution environment on gateways to address the evolution of business models. We present this evolution and summarize existing solutions for execution environments and management for home gateways. Then we propose two improvements that reflect the new requirements. The first improvement is a high-level virtualization of service gateways, and the second one recommends an end-to-end dynamic multiprovider management system. [ABSTRACT FROM AUTHOR]

Although network management has always played a key role for industry, it only recently received a similar level of attention from many research communities, accelerated by funding opportunities from new initiatives, including the FP7 Program in Europe and GENI/FIND in the United States. Work is ongoing to assess the state of the art and identify the challenges for future research in the field, and this article contributes to this discussion. It presents major findings from a two-day workshop organized jointly by the IRTF/NMRG and the EMANICS Network of Excellence, at which researchers, operators, vendors, and technology developers discussed the research directions to be pursued over the next five years. The workshop identified several topic areas, including management architectures, distributed real-time monitoring, data analysis and visualization, ontologies, economic aspects of management, uncertainty and probabilistic approaches, as well as understanding the behavior of managed systems. [ABSTRACT FROM AUTHOR]

In 1995, the IEEE approved the 802.12 standard for data transmission at 100-Mbit/s using the Demand Priority Net- work Access protocol. 100VG-AnyLAN products conforming to this standard offered an upgrade path for Ethernet and Token Ring networks, without requiring new building wiring. A key factor in the approval of the 802.12 standard was the demonstrated error detection properties of its coding scheme. In particular, the coding scheme allows the detection of error bursts affecting encoded data carried on four parallel conductors, using nothing more than the standard IEEE 32-bit cyclic redundancy check applied to the unencoded data. Although these error detection properties were presented for verification as part of the standards process, for many years commercial considerations prevented public disclosure of how the code was actually found. These considerations no longer apply, and, in this paper, we explain in detail the design principles of the code, combining geometrical insight, linear algebra, combinatorial reasoning, and computer search. [ABSTRACT FROM AUTHOR]

We propose to use IEEE 802.22 networks as a natural interconnection between energy-constrained networks, such as sensor networks, and the Internet. In this interconnection scenario, we propose Activecast, broadcast designed as a continuation of the IEEE 802.22 broadcast on sensor networks. Activecast effectively transmits a query to all active sensors in the network. Activecast minimizes the number of retransmitted messages while maintaining high reachability. Activecast requires minimum communication overhead, yet performs very well in the presence of various environmental constrains. Activecast can also be integrated to any sleep based sensor protocol, as it does not make any assumptions on the underlying wake up scheduling protocol and wake up times/durations of the sensors. We study the properties of Activecast by analysis and simulations while also considering irregular radio coverage of sensors. [ABSTRACT FROM AUTHOR]

In this paper, complex cochannel interference of an aeronautical communication system operating in a heavy-traffic environment of 3000 aircraft is modeled and analyzed using a visualization method. This method transforms the cochannel interference, which is specified in terms of message overlaps, from a visual representation to a matrix representation of message overlaps for further statistical analysis. We show that the statistical Poisson distribution provides the best estimates for the message-overlap statistics results. In addition, its cumulative distribution is found to provide useful information regarding the multimessage-decoding capability of a special type of receiver. The results demonstrate that message-overlap statistics could aid in determining the best approach for mitigating cochannel interference. [ABSTRACT FROM AUTHOR]

The present view of medical environments, where isolated networks are used for IT and medical applications, is changing toward an integrated heterogeneous network scenario that can support a wide range of applications. WPAN and WLAN technologies will play a fundamental role in enabling such integrated environment that is expected to support both medical and nonmedical applications. The ultimate goal is to exploit WPAN and WLAN technologies, as well as other wireless networks, such as 3G cellular systems and satellite networks, to support highly efficient medical care delivery, anytime and anywhere. However, the life-critical nature of some medical applications imposes additional challenges that have not been considered in nonmedical scenarios. This article discusses some future scenarios where WLAN and WPAN technologies can be used to provide an integrated and ubiquitous network in medical environments, and identifies the main issues to be addressed in order to meet the QoS requirements of different medical applications when operating in integrated environment. [ABSTRACT FROM AUTHOR]

We evaluate the performance of realistic wireless sensor networks in indoor scenarios. Most of the considered networks are formed by nodes using the Zigbee communication protocol. For comparison, we also analyze networks based on the proprietary standard Z-Wave. Two main groups of network scenarios are proposed: (i) scenarios with direct transmissions between the remote nodes and the network coordinator, and (ii) scenarios with routers, which relay the packets between the remote nodes and the coordinator. The sensor networks of interest are evaluated considering different performance metrics. In particular, we show how the received signal strength indication (RSSI) behaves in the considered scenarios. Then, the network behavior is characterized in terms of end-to-end delay and throughput. In order to confirm the experiments, analytical and simulation results are also derived. [ABSTRACT FROM AUTHOR]

We study the problem of how resilient networks are to node faults. Specifically, we investigate the question of how many faults a network can sustain and still contain a large (i.e., linear-sized) connected component with approximately the same expansion as the original fault-free network. We use a pruning technique that culls away those parts of the faulty network that have poor expansion. The faults may occur at random or be caused by an adversary. Our techniques apply in either case. In the adversarial setting we prove that for every network with expansion $\alpha,$ a large connected component with basically the same expansion as the original network exists for up to a constant times $\alpha \cdot n$ faults. We show this result is tight in the sense that every graph G of size n and uniform expansion $\alpha(\cdot)$ can be broken into components of size o(n) with $\omega(\alpha(n) \cdot n)$ faults. Unlike the adversarial case, the expansion of a graph gives a very weak bound on its resilience to random faults. While it is the case, as before, that there are networks of uniform expansion $\Omega(1/{\rm log}\, n)$ that are not resilient against a fault probability of a constant times $1/{\log}\, n,$ it is also observed that there are networks of uniform expansion $O(1/\sqrt{n})$ that are resilient against a constant fault probability. Thus, we introduce a different parameter, called the span of a graph, which gives us a more precise handle on the maximum fault probability. We use the span to show the first known results for the effect of random faults on the expansion of d-dimensional meshes. [ABSTRACT FROM AUTHOR]

Distributed queuing is a fundamental coordination problem that arises in a variety of applications, including distributed directories, totally ordered multicast, and distributed mutual exclusion. The arrow protocol is a solution to distributed queuing that is based on path reversal on a pre-selected spanning tree of the network. We present a novel and comprehensive competitive analysis of the arrow protocol. We consider the total cost of handling a finite number of queuing requests, which may or may not be issued concurrently, and show that the arrow protocol is $O(s\cdot \log D)$ -competitive to the optimal queuing protocol, where s and D are the stretch and the diameter, respectively, of the spanning tree. In addition, we show that our analysis is almost tight by proving that for every spanning tree chosen for execution, the arrow protocol is $\Omega(s \cdot \log(D/s)/{\log}\log(D/s))$ -competitive to the optimal queuing protocol. Our analysis reveals an intriguing connection between the arrow protocol and the nearest neighbor traveling salesperson tour on an appropriately defined graph. [ABSTRACT FROM AUTHOR]

The article presents a study regarding adding network-layer intelligence to mobile receivers for solving spurious (Transmission Control Protocol) TCP timeout during vertical handoff. It tackles the spurious timeout problem frequently associated with handovers from fast to slow links. TCP sessions can remain active and handoff packet loss can be avoided with the help of Mobile IP/IPv6 and soft handoff however, TCP still faces several performances degradation issues due to the disparities in bandwidth and propagation delays between different access networks particularly during vertical handoffs, some undesirable phenomena may erroneously trigger TCP congestion-control actions and thus degrade TCP performance.

Abstract: The current trend in telecommunications networks addresses an All-IP vision, since most user applications are based on IP, and additionally, IP networks operation is simpler than other more complex ones. These new trends in multimedia communications are giving rise to an increasing need of quality of service (QoS). The Differentiated Services (DiffServ) QoS architecture will provide the means to help underlying technologies, like MPLS, to guarantee the QoS required to support data and real-time services. In DiffServ, QoS is mainly provided with traffic control at edge nodes, and this task is carried out by traffic conditioners. In this paper, we introduce a new policy function for traffic conditioning. Its ability to react to new network conditions makes end-users to get excess bandwidth in proportion to their contracted target rates. We call this method Proportional Excess Traffic conditionER (PETER). Through extensive simulations, we confirm the effectiveness of our approach in providing both a proportional excess bandwidth distribution and assured contracted target rates. [Copyright &y& Elsevier]

In this paper, we present an energy conservation scheme for wireless ad hoc and sensor networks using gossiping to place nodes in an energy saving sleep state. The technique is termed the Gossip-based Sleep Protocol (GSP).With GSP, each node randomly goes to sleep for some time with gossip sleep probability p. GSP is based on the observation that in a well connected network there are usually many paths between a source and destination, so a percentage of nodes can be in an energy conserving sleep mode without losing network connectivity. GSP needs few operations, scales to large networks and does not require a wireless node to maintain the states of other nodes. We propose two versions of GSP, one for synchronous networks and one for asynchronous networks, and afterward extend GSP to adapt to network traffic conditions. We show the advantages of the GSP approach through both simulations and analysis. [ABSTRACT FROM AUTHOR]

Self-organization is critical for a distributed wireless sensor network due to the spontaneous and random deployment of a large number of sensor nodes over a remote area. Such a network is often characterized by its abilities to form an organizational structure without much centralized intervention. An important design goal for a smart sensor network is to be able have an energy- efficient, self-organized configuration of sensor nodes that can scan, detect, and track targets of interest in a distributed manner. In this paper, we propose a novel self-organization protocol and describe other relevant, indigenous building blocks that can be combined to build integrated surveillance applications for self-organized sensor networks. Experiments in both simulated and real-world platforms indicate that this protocol can be useful for tracking targets that follow a predictable course. [ABSTRACT FROM AUTHOR]

In the previous article [1], via experimental studies, we have analyzed the performance of a TCP/IP layered architecture in multihop ad hoc networks. The experimental results point out that a legacy protocol stack does not operate efficiently in ad hoc networks, and cross layering is a promising approach to improve the performance. Cross layering opens a second phase in the ad hoc network design. In this article we present the cross-layer architecture and related protocols, developed in the MobileMAN project. By implementing a full prototype of this architecture, we show that it significantly outperforms a legacy TCP/IP layered architecture. [ABSTRACT FROM AUTHOR]

The deployment of desktop videoconferencing, also known as video and voice over IP (VVoIP), over existing IP networks is gaining popularity. Such a deployment has become a major and challenging task for data network researchers and designers. An analytic approach for deploying videoconferencing is presented. The approach utilises queueing network analysis and investigates two key performance bounds for videoconferencing: delay and bandwidth. The approach can be used to assess the support and readiness of an existing IP network. Prior to the purchase and deployment of desktop videoconferencing equipment, the approach predicts the number of videoconferencing sessions or calls that can be sustained by an existing network while satisfying QoS requirements of all network services and leaving adequate capacity for future growth. As a case study, we apply our approach to a typical network of a small enterprise. In addition, we use OPNET network simulator to verify and validate our analysis. Results obtained from analysis and simulation are in line and give a close match. [ABSTRACT FROM AUTHOR]

Quality-of-service (QoS) signaling protocols for mobile ad hoc networks (MANETs) are highly vulnerable to attacks. In particular, a class of denial-of-service (DOS) attacks can severely cripple network performance with relatively little effort expended by the attacker. A distributed QoS signaling protocol that is resistant to a class of DoS attacks on signaling is proposed. The signaling protocol provides QoS for real-time traffic and employs mechanisms at the medium access control (MAC) layer, which serve to avoid potential attacks on network resource usage. The key MAC layer mechanisms that provide support for the QoS signaling scheme include sensing of available bandwidth, traffic policing, and rate monitoring, all of which are performed in a distributed manner by the mobile nodes. The proposed signaling scheme achieves a compromise between signaling protocols that require the maintenance of per-flow state and those that are completely stateless. The signaling scheme scales gracefully in terms of the number of nodes and/or traffic flows in the MANET. The authors analyze the security properties of the protocol and present simulation results to demonstrate its resistance to DoS attacks. [ABSTRACT FROM AUTHOR]

This paper concerns the comparative performance evaluation of protocols for clustering and backbone formation in ad hoc networks characterized by a large number of resource-constrained nodes. Our aim is twofold: We provide the first simulation-based detailed investigation of techniques for clustering and backbone formation that are among the most representative of this area of ad hoc research. Second, we delve into the nature of the selected protocols to assess the effects of the "degree of localization" on their operations, i.e., how being able to execute the protocol based only on local information affects the overall protocol performance. Extensive ns2-based simulation results show that highly localized protocols are rewarded with good performance with respect to all metrics of interest which include protocol duration, energy consumption, message overhead, route length, and backbone size. [ABSTRACT FROM AUTHOR]

In our study, we investigate a packet-level protocol parallelization approach, which works by parallel multithreading the protocol execution such that packets within and among connections are processed in parallel using distinct processors/threads. The major advantage of this approach is its high scalability—with proper scheduling, more protocol connections, and hence more requests, can be supported by using more threads. In this paper, we present results of our detailed simulations using the NS-2 platform for reliably transferring video stream data in a client-server system. Different types of parameters are used to measure the performance. The parameters include available network bandwidth, different number of TCP connections, and different video sources. Our results show that a parallel approach can indeed significantly enhance the playback quality. [ABSTRACT FROM AUTHOR]

The recently developed H.264 video standard achieves efficient encoding over a bandwidth ranging from a few kilobits per second to several megabits per second. Hence, transporting H.264 video is expected to be an important component of many wireless multimedia services, such as video conferencing, real-time network gaming, and TV broadcasting. However, due to wireless channel characteristics and lack of QoS support, the basic 802.11-based channel access procedure is merely sufficient to deliver non-real-time traffic. The delivery should be augmented by appropriate mechanisms to better consider different QoS requirements and ultimately adjust the medium access parameters to the video data content characteristics. In this article we address H.264 wireless video transmission over IEEE 802.11 WLAN by proposing a robust cross-layer architecture that leverages the inherent H.264 error resilience tools (i.e., data partitioning); and the existing QoS-based IEEE 802.11e MAC protocol possibilities. The performances of the proposed architecture are extensively investigated by simulations. Results obtained indicate that compared to 802.11 and 802.11e, our cross-layer architecture allows graceful video degradation while minimizing the mean packet loss and end-to-end delays. [ABSTRACT FROM AUTHOR]

In this paper, the session setup delay of the session initiation protocol (SIP) is studied. The transmissions on both the forward and reverse channel are assumed to experience Markovian errors. The session setup delay is evaluated for different transport protocols, and with the use of the radio link protocol (RLP). An adaptive retransmission timer is used to optimize SIP performances. Using numerical results, we find that SIP over user datagram protocol (UDP) instead of transport control protocol (TCP) can make the session setup up to 30% shorter. Also, RLP drastically reduces the session setup delay down to 4 to 5 s, even in environments with high frame error rates (10%) and significant correlation in the fading process (fDT = 0.02). SIP is compared with its competitor 11.323. SIP session setup delay with compressed messages outperforms H.323 session setup delay. [ABSTRACT FROM AUTHOR]

In this paper, we consider the problem of how to optimally support multiple concurrent video sessions in an ad hoc network. Specifically, we present a framework on modeling the end-to-end video distortion as a function of routing layer behavior. Our formulation seamlessly integrates the interactions of competing video flows and network layer performance metrics, thus allowing optimal utilization of network resource. We describe a detailed solution procedure based on genetic algorithms (GAs), which allows joint determination of near-optimal routes and rates for the video sessions. We also present a greedy heuristic algorithm that can produce near-optimal solutions and speed up the GA computation. Through simulation results, we demonstrate the superior performance of the GA-based approach. [ABSTRACT FROM AUTHOR]

The problem of operation and maintenance (OAM) in optical burst switched (OBS) networks is not addressed by the optical-networking community even though OBS has been gaining research interest in recent years. In this paper, we introduce a functional model of OBS networks and an OAM architecture that is designed to meet the operational requirements based on this model. We present the first framework to realize OAM in OBS networks, including OAM activities, OAM-aware OBS nodes, OAM information and communication models and protocols. A number of practical examples of possible network failures and the corresponding reactions are presented. [ABSTRACT FROM AUTHOR]

Video streaming over IP networks faces many challenges due to the varying network conditions such as time-varying packet loss and fluctuating bandwidth. In this paper, we focus on streaming scalable video over IP networks in order to enhance the received video quality. We present an adaptive video transmission scheme which combines unequal loss protection and layer selecting. In this scheme, we estimate the packet loss effects on video quality using model-based distortion estimation approach, both for the base layer and the enhancement layers. Based the estimated distortion, the scheme adaptively assigns the unequal amount of forward error correction to each layer and adjusts the sending rate by dynamically selecting the appropriate number of layers to transmit, according to the packet loss rate and the available network bandwidth. The scheme can provide a graceful degradation of received video quality as packet loss increasing and available bandwidth decreasing. Simulations results show that our scheme can provide reasonable video quality under varying network conditions. [ABSTRACT FROM AUTHOR]

The routing of traffic between Interact domains, or Autonomous Systems (ASs), a task known as interdomain routing, is currently handled by the Border Gateway Protocol (BGP). In this paper, we address the problem of interdomain routing from a mechanism-design point of view. The application of mechanism-design principles to the study of routing is the subject of earlier work by Nisan and Ronen [16] and Hershberger and Suri [12]. In this paper, we formulate and solve a version of the routing-mechanism design problem that is different from the previously studied version in three ways that make it more accurately reflective of real-world interdomain routing: (1) we treat the nodes as strategic agents, rather than the links; (2) our mechanism computes lowest-cost routes for all source-destination pairs and payments for transit nodes on all of the routes (rather than computing routes and payments for only one source-destination pair at a time, as is done in [12, 16]); (3) we show how to compute our mechanism with a distributed algorithm that is a straightforward extension to BGP and causes only modest increases in routing-table size and convergence time (in contrast with the centralized algorithms used in [12, 16]). This approach of using an existing protocol as a substrate for distributed computation may prove useful in future development of Internet algorithms generally, not only for routing or pricing problems. Our design and analysis of a strategyproof, BGP-based routing mechanism provides a new, promising direction in distributed algorithmic mechanism design, which has heretofore been focused mainly on multicast cost sharing. [ABSTRACT FROM AUTHOR]

This study proposes an algorithm of the maximum value accumulation method that uses the SNMP MIB II to calculate the line utilization on a network based on TCP/IP protocol. There are four types of algorithms to calculate it; the utilization accumulation method, the utilization midterm calculation method, the maximum calculation method, and the maximum accumulation method. The first two methods are not suitable to detect the faults or process the transmission delays in that they are to be followed by their line utilization, if applicable. On the contrary, the other two whose calculations are based on their accumulated amount of bytes, can be used to not only detect the faults but also compensate for the packet delays. The calculations of the line utilization have their practical uses in the capacity planning, the best calculation algorithm for which the maximum accumulation method would serve as. Its practicability includes coping with system faults, line and routing faults and wraparound of the MIB variables, along with its availability as an indicator for the bandwidth upgrade. The study includes its comparison of the latter two methods above by collecting the current traffic on a TCP/IP network to work on the characteristics of the proposed algorithm, as would help a network manager understand the current status of the line capacity to use series of data as an indicator in the line capacity planning. [ABSTRACT FROM AUTHOR]

An ad hoc network is a multi-hop wireless network of mobile nodes without fixed infrastructure. Its limited bandwidth and frequently changing topology require that its protocol should be robust, simple and energy conserving. We have proposed PDAODMRP (Passive Data Acknowledgement ODMRP) based on the passive acknowledgement function of data packets. PDAODMRP defines the adjacent un-forwarding nodes of forwarding nodes as pool nodes. With the help of pool nodes, PDAODMRP reduces its local route maintenance scope to at least one-hop. Although PDAODMRP has reduced its control overhead and data delivery delay greatly, it still selects multiple paths between a source and a member. And, its data overhead is still high. Hence, in this paper, we propose EPDAODMRP (Extended PDAODMRP) to extend PDAODMRP. Compared PDAODMRP, EPDAODMRP only selects the shortest path between a source and a member instead of all disjoint paths between a source and a member; its local route maintenance is as strong as that of PDAODMRP, which can amend all link failures. The simulation results show that EPDAODMRP has lower data overhead and lower data delivery delay. [ABSTRACT FROM AUTHOR]

The wireless token ring protocol (WTRP) is a novel medium access control (MAC) protocol for wireless local area net- works (WLANs). In contrast with IEEE 802.11 networks, WTRP guarantees quality of service (QoS) in terms of bounded latency and reserved bandwidth, which are critical in many real-time applications. Compared to 802.11, WTRP improves efficiency by reducing the number of retransmissions due to collisions, and it is more fair as all stations use the channel for the same amount of time. Stations take turns transmitting and give up the right to transmit after a specified amount of time. WTRP is a distributed protocol that supports many topologies, as not all stations need to be connected to each other or to a central station. WTRP is robust against single node failures, and recovers gracefully from multiple simultaneous faults. WTRP is suitable for interaccess point coordination in ITS DSRC, safety-critical vehicle-to-vehicle communications, and home networking, and provides extensions to other networks and Mobile IR [ABSTRACT FROM AUTHOR]

A causal broadcast protocol was proposed earlier in [1]. Two extensions of the protocol were also proposed in order to improve its throughput and bandwidth utilization. In this paper, we show that both extensions are not live, i.e., there may be execution patterns in which processes stop delivering messages. We also show that the algorithm for the second extension does not satisfy the requirements on which its correctness was established. Finally, we provide fixed versions of both extensions and prove their correctness. [ABSTRACT FROM AUTHOR]

This article provides an overview of AT&T's MPLS OAM architecture, and gives examples of operational experience. Hallmarks of the architecture are a single, converged, and integrated MPLS/optical network, and the evolution to fully automated, zero-touch network operation. The Concept of One converged IPIMPLS architecture will reduce operations, development, and capital costs. The Concept of Zero aims to bring full automation for every human-to-computer interaction currently required for setting up and maintaining network services, delivering services to customers in real time with zero defects and cycle time, and supporting both a network as well as an operational environment with six nines reliability. This approach effectively opens the network to the customer, enabling new levels of customer network management, service creation, and ordering, and empowering enterprise customers with the tools to create their own network services as they transform their own internal networks. In the article we describe AT&T's MPLS-enabled services, the corresponding MPLS operations architecture (including MPLS MIBs), our MPLS OAM operational experience, and MPLS OAM evolution needs for MPLS MIB enhancements and new network capabilities. By applying technologies such as artificial intelligence, self-healing/self-identifying network elements, expert systems, rules-based processes, and automatic speech recognition, the architecture will migrate from a predictive network that monitors, correlates, and recommends action; to an adaptive network that monitors, correlates, and takes action; to a cybernated network that has integrated components that dynamically manage by business rules and policies. We give several examples of how AT&T is already investing in and implementing this future vision, and conclude by challenging network researchers, developers, and key industry players to apply new technologies in fully realizing the operational vision. [ABSTRACT FROM AUTHOR]

This article describes OAM in MPLS layer 2 transport networks. MPLS networks used to transport layer 2 traffic are referred to as MPLS layer 2 transport networks. They may be used to connect legacy layer 2 networks and/or provide layer 2 service to a user over a MPLS network. As legacy layer 2 networks migrate to use MPLS for transport, the role of MPLS OAM mechanisms is becoming increasingly important. This is because the converged network must offer the same OAM functionality as existing layer 2 networks. This article emphasizes the importance of end-to-end OAM, while emulating existing layer 2 services using MPLS transport. End-to-end fault detection is described in the context of various layer 2 over MPLS transport network models. The article focuses on state-of-the-art MPLS label switched path and pseudo wire OAM mechanisms being developed by the IETF. This includes fault detection and isolation mechanisms such as LSP-Ping, bidirectional forwarding detection, and virtual circuit connectivity verification. The applicability of each of these mechanisms is given. In some cases it may be possible to carry layer 2 OAM cells end-to-end, while in other cases this may not be possible. The relationship between segment-based OAM mechanisms and end-to-end OAM is described for each of these cases. [ABSTRACT FROM AUTHOR]