A distributed protocol for multi-class QoS provision in noncooperative many-switch systems
This paper presents an architecture for multi-class quality of service (QoS) provision in wide area networks. Users or applications are assumed to be selfish and end-to-end QoS is determined by the service levels received by an application traffic flow at each router or switch along a path. In previous work, we have given a comprehensive analysis of the noncooperative multi-class QoS provision game for single-switch systems showing when Nash equilibria exist and under what conditions they are Pareto and/or system optimal. In this paper, we propose a specific network architecture for facilitating noncooperative and of provision in many-switch systems such as the Internet with emphasis on realizability. We shield the user from having to choose the service classes on the switches along a route-a hard combinatorial optimization problem even assuming perfect knowledge about network state-while preserving the basic premise of selfishness. This is achieved by employing a set of QoS agents installed at routers which act on behalf of an user's traffic flow. The QoS agent intercepts packets entering a switch implementing generalized processor sharing (GPS) packet scheduling-and using only constant space packet header overhead and zero per-connection state at the routers-determines which service class to assign the packet to to satisfy the user's end-to-end QoS requirement at minimum cost. We present simulation results which show that our architecture is able to provide stable, stratified services to application traffic with diverse QoS requirements.

title: Performance evaluation of multiple time scale TCP under self-similar traffic conditions
abstract: Measurements of network traffic have shown that self-similarity is a ubiquitous phenomenon spanning across diverse network environments. In previous work, we have explored the feasibility of exploiting long-range correlation structure in self-similar traffic for congestion control. We have advanced the framework of multiple time scale congestion control and shown its effectiveness at enhancing performance for rate-based feedback control. In this article, we extend the multiple time scale control framework to window-based congestion control, in particular, TCP. This is performed by interfacing TCP with a large time scale module that adjusts the aggressiveness of bandwidth consumpton behavior exhibited by TCP as a function of large time scale network state, that is, information that exceeds the time horizon of the feedback loop as determined by RTT. How to effectively utilize such information—due to its probabilistic nature, dispersion over multiple time scales, and realization on top of existing window-based congestion controls—is a nontrivial problem. First, we define a modular extension of TCP (a function call with a simple interface that applies to various flavors of TCP, e.g., Tahoe, Reno, and Vegas) and show that it significantly improves performance. Second, we show that multiple time scale TCP endows the underlying feedback control with proacativity by bridging the uncertainty gap associated with reactive controls which is exacerbated by the high delay-bandwidth product in broadband wide area networks. Third, we investigate the influence of three traffic control dimensions—tracking ability, connection duration, and fairness—on performance. Performance evaluation of multiple time scale TCP is facilitated by a simulation benchmark environment based on physical modeling of self-similar traffic. We explicate our methodology for disc

title: Robust playout mechanism for Internet audio applications
abstract: In Internet audio applications, delay and delay jitter affect mostly the applications' quality of service. Since packet delays are different and changing over time, the receiver needs to buffer some amount of packets before playout. Therefore, the amount of buffered packets and the timing of playout are very important for the performance of applications. We adopt an autoregressive (AR) model for estimation of packet delay and deploy a robust identification algorithm for adjustment of the parameters of the AR process. In our preliminary experiments, this robust algorithm leads to better performance when the noise is correlated and/or non-stationary, and also it is robust to model uncertainties.

title: On the relationship between file sizes, transport protocols, and self-similar network traffic
abstract: Measurements of LAN and WAN traffic show that network traffic exhibits variability on different scales. We examine a mechanism that gives rise to self-similar network traffic and discuss performance. The mechanism we study is the transfer of files or messages whose size is drawn from a heavy-tailed distribution. In a realistic client/server network the degree to which file sizes are heavy-tailed can directly determine the degree of traffic self-similarity at the link level. This causal relationship is robust relative to changes in network resources, network topology, the influence of cross-traffic, and the distribution of interarrival times. Properties of the transport layer play an important role in preserving and modulating this relationship. The reliable transmission and flow control mechanisms of TCP serve to maintain the long-range dependency structure induced by heavy-tailed file size distributions. In contrast, if a non-flow-controlled and unreliable (UDP-based) transport protocol is used, the resulting traffic shows little self-similarity: although still bursty at short time scales, it has little long-range dependence. Performance implications of self-similarity are discussed as represented by various performance measures. Increased self-similarity as expected, results in degradation of performance. Queueing delay, in particular is discussed. Throughput-related measures such as packet loss and retransmission rate, however increase only gradually with increasing traffic self-similarity as long as reliable, flow-controlled transport protocol is used.

title: pKASSO: Towards Seamless Authentication Providing Non-Repudiation on Resource-Constrained Devices
abstract: PKI is generally considered as the most appropriate solution for e-commerce and mutual authentication, owing to its digital signature and non-repudiation features. Asymmetric key operations of PKI require by far more CPU cycles than a symmetric cryptographic algorithm. It hampers the usability of PKI on resource-constrained devices. To overcome these limitations, we propose a new PKI- based authentication protocol and security infrastructure enhanced with single sign-on and delegation technology for a device with a restricted computing power. Although a conventional delegation mechanism cannot support non-repudiation mechanism against malicious user's behavior, our proposed protocol and security infrastructure can provide the mechanism by devising a referee server that generates binding information between a device and authentication messages, and retains the information in its local storage for future accusation.

title: A Comparative Study of Genetic Search
abstract: We present a comparative study of genetic algorithms and their search properties when treated as a combinatorial optimization technique. This is done in the context of the NP-hard problem MAX-SAT, the comparison being relative to the Metropolis process, and by extension, simulated annealing. Our contribution is twofold. First, we show that for large and diicult MAX-SAT instances, the contribution of cross-over to the search process is marginal. Little is lost if it is dispensed altogether, running mutation and selection as an enlarged Metropolis process. Second, we show that for these problem instances , genetic search consistently performs worse than simulated annealing when subject to similar resource bounds. The correspondence between the two algorithms is made more precise via a decomposition argument, and provides a framework for interpreting our results.

title: Analysis and design of the virtual rate control algorithm for stabilizing queues in TCP networks
abstract: The virtual rate control (VRC) algorithm has been proposed for active queue management (AQM) in TCP networks. VRC, a rate-based control mechanism, responds quickly to traffic changes, thus allowing for high utilization and small loss. It can effectively stabilize both the input rate and the queue length around their target levels. In this paper, we analyze the stability of the VRC algorithm based on a linearized TCP model with time delay and provide a design guideline for parameter setting to make the overall system stable. Finally, we confirm the validity of our analysis and the effectiveness of VRC compared to RED, PI, REM, and AVQ through extensive ns-2 simulations.