Search

The Optical Burst Switching (OBS) technology emerged as an alternative switching paradigm for the optical transport layer. Its biggest disadvantage (high data losses) has been the focus of numerous research papers. This paper proposes a data loss reduction technique, which relies on the combination of global network coordination between network nodes and local contention resolution. Via full-scale network simulation it is demonstrated that the proposed scheme has improved performance in terms of data losses and resource utilization, compared to its constituent mechanisms alone. Furthermore, the effectiveness of the mechanism has proven to be less sensitive to load variations in the medium and high load ranges. Additionally, its complexity and deployment cost are low, due to the absence of immature optical components in the network. [ABSTRACT FROM AUTHOR]

In this paper we discuss the use of the Session Initiation Protocol (SIP) as part of the control plane of an application aware Optical Burst Switching (OBS) network, able to support Grid computing applications. The paper presents the possible alternatives for the architecture of such control plane and reports of an experiment in an existing OBS test-bed where this approach was successfully tested in practice. [ABSTRACT FROM AUTHOR]

This paper describes a metamodeling strategy of Service Level Agreements for Digital Video Broadcasting services based on Service Level Agreement Language(SLAng). The purpose of the paper is to provide a detailed analysis of SLAs in this domain and provide a motivation for modeling and automating their management. We also discuss why precise and machine readable SLAs can improve the levels of automation in SLA Management thereby reducing potential violations. The meta-modeling approach based on the Model Driven Architecture(MDA) described in this paper also simplifies the integration of a SLA Management systems with other infrastructure that delivers the service to the client. [ABSTRACT FROM AUTHOR]

This paper builds on the assumption that in the future, UMTS, HIPERLAN-2 and DVB-T can be three (co-operating) components of a composite radio infrastructure that offers wideband wireless access to broadband IP-based services. Managing the resources of this powerful, composite-radio infrastructure in an aggregate manner, and multi-operator scenario, is a complex task. This paper presents an approach to the overall UMTS, HIPERLAN-2 and DVB-T network and service management problem, providing the internal operation of a system addressing this problem. Key points addressed are the development of an architecture that can jointly optimise the resources of the technologies in the composite radio environment, and the development of open interfaces with Service Provider mechanisms and the heterogeneous managed infrastructure. [ABSTRACT FROM AUTHOR]

This paper presents a QoS evaluation in a DiffServ experimental test-bed scenario. We implemented our field trial using prototypal routers running under Linux OS and we arranged them in order to make possible the interconnection with a remote island of a Multi-domain DiffServ network. The performance evaluation of Real-time applications presented in the paper will make clear how it is possible to provide "mission critical" applications with tool-quality level of service when appropriate algorithm and resource sharing are chosen and when these features are associated with a fair degree of aggregation. As a consequence the paper describes the results by means of a Mean Opinion Score (MOS) evaluation campaign to show how Real-Time applications (such as voice and video conferencing) may suffer for the lack of QoS. [ABSTRACT FROM AUTHOR]

A policy based management networking is a new paradigm used to achieve the network management. This paper presents a new policy based Mobile IP users management architecture based on a Common Open Policy Service (COPS) protocol which is currently deployed for QoS management. This paper introduces a new concept of terminal policy enforcement point (TPEP) which allows the terminal to interact with the network enforcing network policies defined by the network manager; it is a key feature of our architecture. The paper presents also the global architecture to support the mobile IP users requirements based mainly on two extensions of COPS protocol; COPS-SLS [1] for QoS negotiation and COPS-MU/MT [2] for policy based user and terminal mobility management. [ABSTRACT FROM AUTHOR]

CE-ants (Cross Entropy ants) is a distributed, robust and adaptive swarm intelligence system for dealing with path management in communication networks. This paper focuses on strategies for adjusting the overhead generated by the CE-ants as the state of the network changes. The overhead is in terms of number of management packets (ants) generated, and the adjustments are done by controlling the generation rate of ants traversing the network. The self-tuned strategies proposed in this paper detect state changes implicitly by monitoring parameters and ant rates in the management system. Rate adaptation is done both in the network nodes and in the peering points of the virtual paths. The results are promising, and compared to fixed rate strategies the self-tuned strategies show a significant saving (70-85%) in number of packets, and has similar (even slightly better) data packet delay and service availability. The rate adaptation in network nodes provides fast restoration with short path detection times and hence also high service availability. The implicit self-tuned ant rate in the path endpoints improves the convergence time on link state events without flooding the network with management packets in steady state when these are not required. Keywords: Cross Entropy, swarm intelligence, CE-ants, network management, restoration time, service availability. [ABSTRACT FROM AUTHOR]

Some systems discard messages that wait in the queue longer than a certain threshold. Identifying such messages and discarding them takes the processor a fixed amount of time. That time is considerably smaller than an average service time, but greater than zero, therefore the models for queuing systems with reneging do not apply. This paper provides a model for such queues. It describes a method of deriving exact formulas for the distribution of waiting times, and proposes simple, yet accurate approximations. The paper then analyzes the model and discusses the properties of such systems. [ABSTRACT FROM AUTHOR]

Under the assumption that packets are sufficiently interleaved and the sampling rate is small, we show in this paper that those characteristics of flows like the number of packets, volume, etc. obtained through deterministic 1-out-of-k packet sampling is equivalent to random packet sampling with rate p = 1/k. In particular, under mild assumptions, the tail distribution of the total number of packets in a given flow can be estimated from the distribution of the number of sampled packets. Explicit theoretical bounds are then derived by using technical tools relying on bounds of Poisson approximation (Le Cam's Inequality) and refinements of the central limit theorem (Berry-Essen bounds). Experimental results from an ADSL traffic trace show good agreement with the theoretical results established in this paper. [ABSTRACT FROM AUTHOR]

Network traffic measurements can provide essential data for network research and operation. While Internet traffic has been heavily studied for several years, there are new characteristics of traffic having not been understood well brought by new applications for example P2P. It is difficult to get these traffic metrics due to the difficulty to measurement traffic on line for high speed link and to identify new applications using dynamic ports. In this paper, we present a broad overview of Internet traffic of an operated OC-48 export link of a metro area network from a carrier with the method of measurement on-line. The traffic behaves a daily characteristic well and the traffic data of whole day from data link layer to application layer is presented. We find the characteristics of traffic have changed greatly from previous measurements. Also, we explain the reasons bringing out these changes. Our goal is to provide the first hand of traffic data that is helpful for people to understand the change of traffic with new applications. [ABSTRACT FROM AUTHOR]

For a broad class of polling models the evolution of the system at specific embedded polling instants is known to constitute a multi-type branching process (MTBP) with immigration. In this paper it is shown that for this class of polling models the vector ${\underline{X}}$ that describes the state of the system at these polling instants satisfies the following heavy-traffic behavior, under mild assumptions: 1$$ \label{eq01} (1-\rho){\underline {X}} \rightarrow_d {\underline {\gamma}}~\Gamma(\alpha, \mu)~~~~(\rho \uparrow 1), $$ where ${\underline {\gamma}}$ is a known vector, Γ(α, μ) has a gamma-distribution with known parameters α and μ, and where ρ is the load of the system. This general and powerful result is shown to lead to exact - and in many cases even closed-form - expressions for the Laplace-Stieltjes Transform (LST) of the complete asymptotic queue-length and waiting-time distributions for a broad class of branching-type polling models that includes many well-studied polling models policies as special cases. The results generalize and unify many known results on the waiting times in polling systems in heavy traffic, and moreover, lead to new exact results for classical polling models that have not been observed before. As an illustration of the usefulness of the results, we derive new closed-form expressions for the LST of the waiting-time distributions for models with a cyclic globally-gated polling regime. As a by-product, our results lead to a number of asymptotic insensitivity properties, providing new fundamental insights in the behavior of polling models. [ABSTRACT FROM AUTHOR]

In this paper we investigate the maximum message throughput of the ActiveMQ server in different application scenarios. We use this throughput as a performance criterion. It depends heavily on the installed filters and the message replication grade. In previous work, we have presented measurement results and an analytical model for simple filters. This work extends these studies towards more complex configuration options. It provides measurement results and analytical performance models for complex AND-, OR-, and IN-filters. The results are useful to understand the performance of JMS servers and help to dimension large distributed JMS-based systems. [ABSTRACT FROM AUTHOR]

This paper presents the results of a simulation study that assessed SIP based VOIP networks under overload. This work addresses the issue of network level congestion controls in SIP based telephony networks. The simulation network consists of Media Gateways and Call Controllers, each with internal overload detection and control mechanisms. The simulation includes SIP timers tuned to operate gracefully with PSTN interfacing protocols. The traffic model is SIP based VoIP calls not involving application server or media server interactions. This work demonstrates that combining external overload controls with internal overload controls reduces blocking and increases goodput across the overload levels that ranged from 1 to 4 times the engineered load. [ABSTRACT FROM AUTHOR]

In some specific applications, sensors can be deployed in a deterministic way to form regular network. This paper firstly analyzes the relationship between the probability of coverage and that of the node failure in the network with triangular topology. Then the fault tolerance performance in triangular topology network is analyzed by using the k-subnet. At last, the paper discusses the connectivity performance in triangular topology network and in grid topology network. [ABSTRACT FROM AUTHOR]

In the paper a performance evaluation model of mobile wireless sensor network is presented. The model is based on renewal theory. The hierarchical structure of the network holds a clusters composed of ordinary sensors. Afterwards, all clusterhead sensors belong to a backbone network which is needed for data transmission to the sink of the sensor network. Some sensors are mobile and can send their data to the clusterhead sensors. In this paper, we address one of the fundamental problems, namely performance modeling of mobile wireless sensor networks. Moreover, our model can also be used for ordinary wireless sensor networks which are static and geometrically constrained. Specific models are suggested and analysed for different communication needs. [ABSTRACT FROM AUTHOR]

This paper discusses different capacity leasing scenarios for the optical network. It aims at providing systematic understanding of cost structure of optical networks, without focusing on technical details. It reviews different kinds of capacity leasing approaches discussing the relative costs and the flexibility associated to them to adapt to future traffic needs. Then it applies the Real Options principles to evaluate the most convenient planning solution. Real Option valuation is shown to be the formalization of the natural way of valuating different alternatives under uncertainty, taking into account that information becoming available during the course of the planning horizon might influence the strategy followed. The goal of the paper is to give insight in the practical applicability of the technique for the network operator. [ABSTRACT FROM AUTHOR]

Today's data transport networks are evolving continuously towards customer oriented and application aware networks. This evolution happens in Europe in a highly diverse network environment, covering multiple network domains, layers, technologies, control and management approaches. In this paper, the issues, challenges and the solutions developed in the IST project MUPBED (,,Multi-Partner European Test Beds for Research Networking"; www.ist-mupbed.eu) for seamless interworking in a typical European heterogeneous network environment are described, addressing horizontal, interdomain, and vertical, inter-layer topics related to data plane, control plane and applications. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to assess the impact of timer-based burst assembly algorithms for TCP traffic. We present an analysis for short, medium and long assembly times and investigate segment and flow distribution over the assembled bursts. Further, we also analyze their impact on the congestion window evolution and on the effective throughput achieved. It has been found out that short assembly times are ideally suitable for sources with small congestion windows, allowing for a speed up, while large assembly times yield a lower throughput variation among the individual assembled flows. For long assembly times, the transfer of more segments from the same source is trading off the increase of the burstification delay but no throughput gain is obtained. However, large assembly times smooth out individual flow performance and provide a significant lower variation of throughput. To this end, in this paper, we propose a new adaptive burst assembly algorithm that dynamically assigns flows to different burstifiers based on their instant window size. [ABSTRACT FROM AUTHOR]

This paper proposes 80Gb/s multi-wavelength optical packet switching(OPS) using a PLZT switch. The Multi-wavelength OPS Network can achieve low implementation costs compared to existing OPS networks in which the number of wavelengths is large. In this network, the header is processed separately from the payload. The payload is divided into multiple segments. Each segment is then encoded into different wavelengths. After assignment of wavelength to each payload segment, payload segments are multiplexed into an optical signal which is then transmitted through an optical fiber. Therefore, the number of components required for intermediate node functionality stays the same for the number of wavelengths used for payload transmission. This paper shows a fundamental experiment of the Multi-wavelength OPS network using a PLZT switch. PLZT switch provide a fast optical switching with low noise, independent polarization, and low drive voltage. In this paper, we describe the detail of the experiments and results. [ABSTRACT FROM AUTHOR]

The justification for using mutihop clusters may be found in [1]. In the well known heuristic proposed in [2], the d-dominating set of clusterheads is first selected by using nodes identifiers and then clusters are formed. In this paper we generalise this algorithm in order to select nodes depending of a given criterion (as the the degree, density or energy of nodes). The first section of this paper simplifies and proves the correctness of our generalised algorithm to select clusterheads. The cluster formation process proposed in [2] is extensively studied in the second section and is proved to be false. [ABSTRACT FROM AUTHOR]

Recently, Doubletree, a cooperative algorithm for large-scale topology discovery at the IP level, was introduced. Compared to classic probing systems, Doubletree discovers almost as many nodes and links while strongly reducing the quantity of probes sent. This paper examines the problem of the nodes and links missed by Doubletree. In particular, this paper's first contribution is to carefully describe properties of the nodes and links that Doubletree fails to discover. We explain incomplete coverage as a consequence of the way Doubletree models the network: a tree-like structure of routes. But routes do not strictly form trees, due to load balancing and routing changes. This paper's second contribution is the Windowed Doubletree algorithm, which increases Doubletree's coverage up to 16% without increasing its load. Compared to classic Doubletree, Windowed Doubletree does not start probing at a fixed hop distance from each monitor, but randomly picks a value from a range of possible values. [ABSTRACT FROM AUTHOR]

This paper compares several approaches for dynamic allocation in geo-stationary networks based on DVB-RCS system. Each Satellite Terminal (ST) regularly sends requests to the Network Control Center (NCC) which in turn allocates resource to the users. Unfortunately, this delayed request-assignment makes the dynamic bandwidth allocation very difficult. Simple mechanisms such as a fixed allocation or requests based on the current size of the terminals' queue are compared to predictive methods based on control theory techniques which have been previously proposed. A lower bound is also derived by considering that the actual size of the buffer can be instantaneously known. It is shown that if the traffic is not really bursty, a fixed allocation which implies lighter signalling mechanisms leads to good results. In bursty traffic conditions, simple mechanisms for which the requests correspond to the actual size of the buffer may lead to the best performance results. [ABSTRACT FROM AUTHOR]

This paper investigates the use of cooperative communications in the context of IEEE 802.11b to combat radio signal degradation. The performance gain of both an existing cooperative protocol and the one proposed in the paper is discussed. It is quantitatively shown how much the two cooperative protocols increase throughput, lower delivery latency, and extend transmission span, when compared to the conventional IEEE 802.11b protocol. These features may help improve connectivity and network performance in ad hoc applications. [ABSTRACT FROM AUTHOR]

Two main steps on the way to more realistic simulations of mobile ad-hoc networks are the introduction of realistic mobility and sophisticated radio wave propagation models. Both have strong impact on the performance of mobile ad-hoc networks, e.g. the performance of routing protocols changes with these models. In this paper we introduce a framework which combines realistic mobility and radio wave propagation models. Our approach consists of a zone-based mobility generator and a high accuracy radio wave propagation model. For the mobility generation a wide variety of well understood random mobility models is combined with a graph based zone model, where each zone has its own mobility model. To achieve a realistic radio wave propagation model a ray tracing approach is used. The integration of these two techniques allows to create simulation setups that closely model reality. [ABSTRACT FROM AUTHOR]

In this paper we describe a self-organising and self-managing system for a Cooperative Service Provisioning (CSP) of media transport and processing services. The term cooperative is used since we assume that CSP providers as well as users offer resources to be utilised for media delivery and processing based on an Overlay Network principle. The core building block of the proposed system is a Distributed Hash Table extended with a CSP specific indexing principle and recursive search algorithm. The task of QoS constraint verification for a requested service is distributed between participating nodes. In this paper we describe CSP based on a Content Addressable Network (CAN) [1] DHT. The resulting system is evaluated based on a theoretical analysis as well as simulations. [ABSTRACT FROM AUTHOR]

One of TCP's key tasks is to react and avoid network congestion episodes which normally arise in packet switched networks. A wide literature is available concerning the behaviour of congestion control algorithms in many different scenarios and several congestion control algorithms have been proposed in order to improve performances in specific scenarios. In this paper we focus on the UMTS wireless scenario and we report a campaign of measurements that involved around 3000 flows and more than 40 hours of measurements using three different TCP stacks: TCP NewReno, which is the congestion control algorithm standardized by IETF, TCP BIC which is the default congestion control algorithm adopted by the Linux operating system, and TCP Westwood+ also available in the Linux kernel. The experimental evaluation has been carried out by accessing the public Internet using an UMTS card. Measurements of goodputs, RTTs over time, packet loss ratios, number of timeouts and Jain Fairness Indices are reported through cumulative distribution functions. Moreover, the efficiency of each TCP version in transferring files has been evaluated by varying the file size in the range from 50 KB up to 500 KB. The cumulative distribution functions reported in the paper show interesting results: 1) a single downlink flow is far from saturating the channel bandwidth; 2) considered TCP stacks provide similar results; 3) 90th (50th) percentile of the goodput of a single downlink flow is less or equal then 230 kbps (120 kbps) compared to a nominal 384 kbps UMTS downlink channel. [ABSTRACT FROM AUTHOR]

This paper provides an overview and comparison of traditional and advanced Link-to-System (L2S) interface mappings used in system level simulations to evaluate link performance in terms of packet error rate (PER). An Actual Value Interface (AVI) as traditional L2S interface is compared with an Effective SINR Mapping (ESM) as advanced L2S interface. This comparison is able to highlight the main differences in prediction of multi-state channel performance effecting on final data throughput, delay of data packets and required CPU time. Furthermore, this paper proposes an improved version of AVI method in order to improve the accuracy of system performance estimation. The comparison results show that in case of multi-state OFDM system, highest accuracy is achieved with Mutual Information ESM (MIESM) method and relatively good accuracy with the exponential ESM (EESM) method. Keywords: System simulator, L2S interface, EESM, MIESM, AVI, OFDM. [ABSTRACT FROM AUTHOR]

Previous work on energy efficient broadcast protocols for wireless ad hoc networks are based a commonly used physical layer model called "Path-loss model" which assume two nodes can communicate if and only if they exist within their transmission radius. In this paper, we analyze the effect of realistic physical layer on energy efficient broadcast protocols. We employ a more realistic log-normal shadowing model for physical layer and consider two link layer operating models: EER (end-to-end retransmission) and HHR (hop-by-hop retransmission). Networks with omni-antennas and directional antennas are dealt with separately. Based on above models, we analyze how to adjust actual transmission radius for transmission nodes and relay nodes to get the trade-off between maximizing probability of delivery and minimizing energy consumption. From our analysis based on shadowing model, we have derived the appropriate transmission range. The results presented in this paper are expected to improve the performance of broadcast protocols under realistic physical layer. [ABSTRACT FROM AUTHOR]

The 3rd Generation Partnership Project (3GPP) has proposed the IP Multimedia Subsystem (IMS) as a key element in the next-generation network (NGN) converged architecture supporting multimedia services. Extending the IMS towards provisioning support for location based services (LBS) will enable enhanced services and offer new revenues to the system. However, conveying location information in the IMS and connecting the IMS with a real positioning system are still open issues. This paper presents the design and implementation of an IMS Location Server (ILS) integrating IMS with a positioning system. From the IMS perspective, the ILS serves as a service enabler for LBS. Considerable work has been done by the IETF in the area of location information transport based on the Session Initiation Protocol (SIP). This paper proposes some improvements in this area. In order to demonstrate proof-of-concept in enhancing IMS-based services, a Location-aware Push-to-Talk (LaPoC) prototype service has been developed. The service has been integrated and tested with the Ericsson Mobile Positioning System (MPS). The paper also gives the results of performance measurements including traffic load analysis and session establishment time. [ABSTRACT FROM AUTHOR]

The absence of a router or a base station urges the need for better access control mechanism in the ad-hoc networks. This paper presents a localized approach for access control which implements ticket certification services through reputation mechanism. Reputation refers to, the opinion of one node as seen by other nodes. Ticket certification ensures that, only well behaving nodes (which forward and route packets of other nodes) can get the tickets and only they can access the network. The tickets are obtained from any node in the locality with high reputation instead of getting it from a centralized authority or from some k neighbors in the neighborhood. This paper gives the analysis and simulation results of the localized approach through reputation mechanism and proves that the localized access control with reputation is better than the localized approach without reputation. [ABSTRACT FROM AUTHOR]

In this paper, a new QoS model is presented for end-to-end service provisioning in wireless ad hoc networks. Many previous works focus on the packet scheduling mechanism using multiple service classes implemented for traffic prioritization based service differentiation. However, this paper concentrates on a scheme for dynamically selecting a proper one among several forwarding classes that perform different service rate according to service requirements. There service requirements include low delay, high throughput, and low loss. The proposed solution is a new QoS provisioning model called Dynamic Hop Service Differentiation (DHSD). This model supports soft QoS provisioning to reduce network overhead and wireless PHB (WPHB) to achieve the end-to-end QoS required by applications. The proposed QoS model is evaluated using OPNET simulation. We show that this model outperforms both best-effort and strict priority service models in wireless ad hoc network environments. [ABSTRACT FROM AUTHOR]

For multi-hop wireless networks using IEEE 802.11 most TCP performance degradation results from hidden, exposed terminal problems and bandwidth waste caused by exponential backoff of retransmission timer due to node's mobility, not from collisions. However, in normal DCF algorithm, a failed user increases its contention window (CW) exponentially, thus it reduces the success probability of exposed terminal nodes. That is, these problems will cause burst data transmissions frequently in a particular node which already was successful in packet transmission, because the probability of successful packet transmission rate would be increased. To solve these problems, in this paper, we propose an efficient contention window control (ECWC) scheme to increase TCP performance in wireless multi-hop network. The proposed ECWC scheme is suggested to reduce the hidden and exposed terminal problems of wireless multi-hop network. That is, the proposed scheme increases the number of backoff retransmissions to increase the successful probability rate of MAC transmission, and fixes the contention window at a predetermined value. [ABSTRACT FROM AUTHOR]

The ieee 802.11 mac-protocol, often used in ad-hoc networks, has the tendency to share the capacity equally amongst the active nodes, irrespective of their loads. An inherent drawback of this fair-sharing policy is that a node that serves as a relay-node for multiple flows is likely to become a bottleneck. This paper proposes a flow-level performance model of such a bottleneck node using fluid-flow analysis. Assuming Poisson initiations of new flow transfers at the bottleneck node, we obtain insightful, robust, and explicit expressions for characteristics related to the overall flow transfer time, the buffer occupancy, and the packet delay at the bottleneck node. The analysis is enabled by a translation of the behavior of the bottleneck node and the source nodes in terms of an m/g/1 queueing model. We conclude the paper by an assessment of the impact of alternative capacity sharing amongst source nodes and the bottleneck in order to improve the performance of the bottleneck. [ABSTRACT FROM AUTHOR]

Multipath is a sought-after mechanism to achieve reliability along the error-prone channel in wireless sensor networks. However, this technique is not energy efficient since sensor networks are subject to strict resource constraints. In this paper, we propose an energy aware method to combine multipath routing with practical network coding technique. Through this method, we can guarantee the same reliability while reduce much energy consumption by decreasing the number of paths needed to delivery data. This method only needs little metadata overhead and some small-scale linear operations. Simulations under different circumstances verify the theoretical results. The paper also discusses other advantages of network coding in multi-receiver case to illustrate our future work. [ABSTRACT FROM AUTHOR]

The Virtual Home Environment (VHE) has been introduced as an abstract concept enabling users to access and personalize their subscribed services whatever the terminal they use and whatever the underlying network used. The European IST VESPER project (Virtual Home Environment for Service Personalization and Roaming Users) aims to provide an architectural solution and an implementation of the VHE, providing ubiquitous service availability, personalised user interfaces and session mobility, while users are roaming or changing their equipment. In this paper we present a multimedia delivery service, one of the trial services selected to demonstrate VHE features, showing its interconnection with the so far defined VESPER VHE architecture. [ABSTRACT FROM AUTHOR]

The UMTS-FDD system, one of the members of the ITU IMT-2000 third generation standard for terrestrial cellular systems, employs pruned Golay sequences to enable initial synchronisation of the mobile terminals to the network. In this paper a low complexity solution for initial synchronisation is proposed, which is able to counteract the performance degradation introduced by large frequency offsets occurring in the mobile station receiver. Simulation results are provided to validate the proposed solution. [ABSTRACT FROM AUTHOR]

This paper analyzes different packetization strategies that significantly improve the quality of H.263 coded video transmission in wireless local area networks (WLANs). We show that a considerable improvement can be obtained with the proper combination of error concealment techniques and transmission unit (TU) sizes. Moreover, we present performance evaluation results on critical system parameters for interactive video over Ad—Hoc WLANs, and propose a simple rule to specify TU sizes. We use Kinesis, a novel system architecture for packet video, as a software measurement tool to analyze the effects of packetization policies, distance, network offered load, and interference from co—located WLAN devices on overall video quality. Kinesis supports IP multicast extensions, overcoming delay issues introduced by the complex retransmission schemes in the IEEE 802.11 MAC sublayer, which are not acceptable for real—time services. It implements real—time transport protocol functions to manage synchronization and QoS, and performs software—only real—time H.263 video encoding. In this paper we address most common Ad—Hoc WLAN configurations, and present experimental results on Packet Error Rates, Frame Error Rates, frame delays and latency, and Peak Signal-to-Noise Ratio for well—known test video sequences. [ABSTRACT FROM AUTHOR]

In this paper we present a scheme that enables a mobile user to perform a " QoS-conditionalized" handoff when moving to an overlapping area in Mobile IPv6. The idea is to use a QoS hop-by-hop option piggybacked in the binding messages for QoS signaling and conditional-ize a handoff upon the availability of sufficient resources along the new transmission path. Our scheme builds upon the hierarchical mobile IPv6 protocol and is especially suited for micro-mobility. It also enables the mobile node to flexibly choose among a set of available access points so that the mobile node can transmit packets through a route which offers satisfying QoS. [ABSTRACT FROM AUTHOR]

Quality of Service (QoS) for the Internet has been discussed for a long time without any major breakthrough. There are several reasons, the main one being the lack of a scalable, simple, fast and low cost QoS solution. A new QoS-framework, called resource management in differentiated services (RMD), aims to correct this situation. This framework has been published in recent papers and is extending the IETF differentiated services (diffserv) architecture with new admission control and resource reservation concepts in a scalable way. This paper focuses on proposing and investigating two resource reservation solutions on the problem of severe congestion situation within a diffserv-aware network utilizing an admission control scheme called Resource Mananagement in Diffserv (RMD). The different severe congestion solutions are compared using extensive simulation experiments. [ABSTRACT FROM AUTHOR]

It is widely recognized that the maximum number of heavy-tailed flows that can be admitted to a network link, while meeting QoS targets, can be much lower than in the case of markovian flows. In fact, the superposition of heavy-tailed flows shows long range dependence (self-similarity), which has a detrimental impact on network performance. In this paper, we show that long range dependence is significantly reduced when traffic is controlled by a Measurement-Based Admission Control (MBAC) algorithm. Our results appear to suggest that MBAC is a value added tool to improve performance in the presence of self-similar traffic, rather than a mere approximation for traditional (parameter-based) admission control schemes. [ABSTRACT FROM AUTHOR]

The CMPP (Circulant Modulated Poisson Process) modeling approach represents an appealing solution since it provides the integration of traffic measurement and modeling. At the same time, it maintains the Markovian hypothesis that permits analytical transient and steady-state analyses of queueing systems using efficient algorithms. These relevant features of CMPP approach has driven us to analyze in more details the fitting procedure when it is applied to actual broadband traffic. In the paper, investigating the estimation algorithm of model parameters, we emphasize the difficulty of CMPP in capturing the upper tail of marginal distribution of actual data, which leads to an optimistic evaluation of network performance. As shown in the paper, a simple relation exists between the number of significant eigenvalues obtained by the spectral decomposition and the peak rate that the CMPP structure is able to capture. The relation evidences the difficulties of CMPP to model actual traffic, characterized by long tailed distribution, as well as traffic data with the well accepted hypothesis of gaussian marginal. [ABSTRACT FROM AUTHOR]

Understanding the end-to-end packet delay dynamics of the Internet is of crucial importance since it directly affects the QoS (Quality of Services) of various applications, and it enables us to design an efficient congestion control mechanism. In our previous studies, we have measured round-trip time of the Internet, and have modeled its dynamics by the ARX (Auto-Regressive eXogenous) model using system identification. As input and output data for the ARX model, we have used the packet inter-departure time from a source host and the corresponding round-trip time variation measured by the source host. In the current paper, for improving the model accuracy, we instead use the packet transmission rate from the source host and the average round-trip time measured by the source host. Using input and output data measured in working LAN and WAN environments, we model the round-trip time dynamics by determining coefficients of the ARX model using system identification. Through numerical examples, we show that in LAN environment, the round-trip time dynamics can be accurately modeled by the ARX model. We also show that in WAN environment, the round-trip time dynamics can be accurately modeled when the bottleneck link is shared by a small number of users. [ABSTRACT FROM AUTHOR]

Delivering innovative Internet services raises numerous business and technical challenges for providers. It actually requires building and managing complex, distributed architectures in order to reach the quality of service that is needed. In this paper, we argue that using edge computing in the domain of Internet services has a number of advantages. However, this approach relies on complex and hard to administrate environments. We believe that autonomic computing techniques constitute a key element for the dynamic management of edge servers. In the paper, we present an autonomic manager that meets the market needs and that has been tested in collaboration with Bull SA. [ABSTRACT FROM AUTHOR]

Many measurement studies of P2P file sharing systems suggest that the request rate for a file changes over time and the system is thus non-stationary. For this reason we study the population dynamics and the availability of a file in a BitTorrent-like file sharing system, when the arrival rate for file requests decreases exponentially. We study the system first by a deterministic fluid model and then by a more detailed Markov chain analysis that allows estimating the life time of a single chunk exactly. Simple approximation for the life time is also derived. In addition, we simulate the life time of a file consisting multiple chunks in order to verify the analytical results to be applicable also to a more complex system. [ABSTRACT FROM AUTHOR]

Service discovery is a basic requirement for mobile ad hoc networks to provide service efficiently with dynamically changing network topology. In this paper, we propose a service discovery protocol with maximal area disjoint path (SDMAD) for mobile ad hoc networks. The goal of SDMAD is to exploit multiple servers simultaneously and do parallel delivery. One key feature of SDMAD is that there is no contention between the multiple paths discovered by it. Moreover, SDMAD considers service discovery and routing jointly to reduce control overhead. Extensive simulations show that with SDMAD the performance of service delivery is greatly improved over that with other service discovery protocols. [ABSTRACT FROM AUTHOR]

The paper presents a new analytical saturation throughput model of IEEE 802.11 DCF (Distributed Coordination Function) with basic access in ad-hoc mode. The model takes into account freezing of the backoff timer when a station senses a busy channel. It is shown that taking into account this feature of DCF is important in modeling saturation throughput - yields more accurate results than models known from literature. The proposed analytical model also takes into account the effect of transmission errors. [ABSTRACT FROM AUTHOR]

In this paper we evaluate the performance of a content distribution service with respect to reliability and efficiency. The considered technology for realizing such a service can either be a traditional client/server (CS) architecture or a peer-to-peer (P2P) network. In CS, the capacity of the server is the bottleneck and has to be dimensioned in such a way that all requests can be accommodated at any time, while a P2P system does not burden a single server since the content is distributed in the network among sharing peers. However, corrupted or fake files may diminish the reliability of the P2P service due to downloading of useless contents. We compare a CS system to P2P and evaluate the downloading time, success ratio, and fairness while considering flash crowd arrivals and corrupted contents. [ABSTRACT FROM AUTHOR]

Renewed interest in ALOHA-based Medium Access Control (MAC) protocols stems from their proposed applications to wireless ad hoc and sensor networks that require distributed and low complexity channel access algorithms. In this paper, unlike in the traditional work that focused on mean value (throughput) and stability analysis, we study the distributional properties of packet transmission delays over an ALOHA channel. We discover a new phenomenon showing that a basic finite population ALOHA model with variable size (exponential) packets is characterized by power law transmission delays, possibly even resulting in zero throughput. This power law effect might be diminished, or perhaps eliminated, by reducing the variability of packets. However, we show that even a slotted (synchronized) ALOHA with packets of constant size can exhibit power law delays when the number of active users is random. From an engineering perspective, our results imply that the variability of packet sizes and number of active users need to be taken into consideration when designing robust MAC protocols, especially for ad-hoc/sensor networks where other factors, such as link failures and mobility, might further compound the problem. [ABSTRACT FROM AUTHOR]

This paper studies the problem of dimensioning a wireless base station that operates with CAC. It models the base station as a multi-rate, multi-class, multi-resource loss model and proposes two methods for fast estimation of the admission region. The results show that our methods are typically more accurate than other more computationally intensive approximations, such as the reduced-load approximation, and provide an excellent basis for the dimensioning of wireless networks with CAC. [ABSTRACT FROM AUTHOR]