Dynamic Time Windows and Generalized Virtual Clocks-Combined Closed-Loop/Open-Loop Mechanisms for Congestion Control of Data Traffic in High Speed Wide Area Networks

This paper presents a set of mechanisms for congestion control of data traffic in high speed wide area networks (HSWANs) along with preliminary performance results. The model of the network assumes reservation of resources based on average requirements. The mechanisms address (a) the different network time constants (short term and medium-term), (b) admission control that allows controlled variance of traffic as a function of medium-term congestion, and (c) prioritized scheduling which is based on a new fairness criterion. This latter criterion is perceived as the appropriate fairness measure for HSWANs. Preliminary performance studies show that the queue length statistics at switching nodes (mean, variance and max) are approximately proportional to the end-point \u27time window\u27 size. Further, * when network utilization approaches unity, the time window mechanism can protect the network from buffer overruns and excessive queueing delays, and * when network utilization level is smaller, the time window may be increased to allow a controlled amount of variance that attempts to simultaneously meet the performance goals of the end-user and that of the network. The prioritized scheduling algorithms proposed and studied in this paper are a generalization of the Virtual Clock algorithm [Zhang 1989]. The study here investigates * necessary and sufficient conditions for accomplishing desired fairness, * simulation and (limited analytical results for expected waiting times, * ability to protect against misbehaving users, and * relationship between end-point admission control (Time-Window) and internal scheduling (\u27Pulse\u27 and Virtual Clock) at the switch

Experience with Active Congestion Control 1

Active Congestion Control (ACC) applies active networking to feedback congestion control an a high bandwidth-delay product network, shortening the feedback loop by filtering traffic in the network near congestion. This paper describes recent simulation results showing the function of the system in TCP networks across a range of bandwidth-delay products. It also discusses the implementation of another version of the system in the ASP EE, an active networking execution environment implemented at USC/ISI. An assessment of ACC overhead in that implementation is made. Ke ywords: Active Networks, Congestion Control 1

Dynamic Time Windows: Congestion Control and Avoidance in High Speed Networks

This thesis describes the Dynamic Time Windows congestion control and avoidance system. This system is designed to mitigate the effects of network congestion on today's networks and the networks of the future by directly controlling source burstiness. This chapter will discuss the need for congestion control in computer networks, identify the aspects of congestion control that present particular challenges in high speed networks, and introduce the Dynamic Time Windows system (DTW). It will also provide an overview of the remainder of the thesis