This paper presents a control-theoretic approach to reactive flow control in networks that do not reserve bandwidth. We assume a round-robin-like queue service discipline in the output queues of the network’s switches, and propose deterministic and stochastic models for a single conversation in a network of such switches. These models motivate the Packet-Pair rate probing technique, and a provably stable rate-based flow control scheme. A Kalman state estimator is derived from discrete-time state space analysis, but there are difficulties in using the estimator in practice. These difficulties are overcome by a novel estimation scheme based on fuzzy logic. We then present a technique to extract and use additional information horn the system to develop a continuous-time system model. This is used to design a wuisnt of the control law that is also provably stable, and, in addition, takes control action as rapidly as possible. Finally, practical issues such as correcting parameter drift and cmmlination with window flow control are described.

This paper examines the phenomenon of congestion in order to better understand the congestion management techniques that will be needed in high-speed, cell-based networks. The first step of this study is to use high time-resolution local area network (LAN) traffic data to explore the nature of LAN traffic variability. Then, we use the data for a trace-driven simulation of a connectionless service that provides LAN interconnection. The simulation allows us to characterize what congestion might look like in a high-speed, cell-based network. The most

This paper presents the packet-pair rate-based feedback flow control scheme. This scheme is designed for networks where individual connections do not reserve bandwidth and for the available bitrate (best-effort) component of integrated networks. We assume a round-robin-like queue service discipline in the output queues of the network's switches, and propose a linear stochastic model for a single conversation in a network of such switches. These model motivates the Packet-Pair rate probing technique, which forms the basis for provably stable discrete and continuous time rate-based flow control schemes. We present a novel state estimation scheme based on fuzzy logic. We then address several practical concerns: dealing with system startup, retransmission and timeout strategy, and dynamic setpoint probing. We present a finite state machine as well as source code for a model implementation. The dynamics of a single source, the interactions of multiple sources, and the behavior of packet-pai...

The emerging B-ISDN is expected to adopt ATM (asynchronous transfer mode) as the transport network. This new network must support several classes of service with varying delay and loss requirements, such as voice, audio, data, and high quality video. It must also operate with link speeds in the hundreds of megabits per second and be scalable up to potential link speeds on the order of gigabits per second. The requirements to support multiple services and high speed pose problems not previously faced in traditional packet switched networks. Reactive methods of control become less effective due to the large propagation delay-bandwidth product. Packet processing delay becomes noticeably large in relation to the packet transmission time. Priority and other scheduling schemes must be devised to multiplex real-time streams with packet data efficiently and fairly. This paper reviews some of the techniques directed at these issues. 1 Introduction B-ISDN is expected to be introduced into comme...

ATM networks will carry a wide variety of data over the same packet switching network. A majority of this traffic is expected to be real-time video generated by video on demand, video conferencing systems, etc. We study the characteristics of video data compressed using standard coding algorithms namely, JPEG, MPEG and also popular ones such as the video conferencing software NV. A wide range of video sources from movies to a class lecture were analyzed. Most of the traces were longer than an hour. The bit rate of the traces has been characterized using the leaky bucket model. We also show a method of choosing appropriate leaky bucket parameters. Burstiness function is used to characterize the burstiness of the video traffic at different time scales. Our studies indicate that JPEG compressed has very little short term burstiness. MPEG and NV traffic shows high burstiness over small time scales. JPEG and MPEG video exhibit burstiness over long time scales, whereas NV shows no burstiness...

Maximizing bandwidth utilization and providing performance guarantees, in the context of multimedia networking, are two incompatible goals. Heterogeneity of the multimedia sources calls for effective traffic control schemes to satisfy their diverse Quality of Service(QoS) requirements. These include admission control at connection set up, traffic control at the source ends and efficient scheduling schemes at the switches. The emphasis in this paper is on traffic control at the source end. Most multimedia sources are bursty in nature. Traffic shapers have been mainly studied hitherto from the point of view of their effectiveness in smoothing the burstiness. Leaky Bucket(LB) scheme, to cite an example, is a mean rate policer smoothing at the token generation rate. Studies on bursty sources show that burstiness promotes statistical multiplexing at the cost of possible congestion. Smoothing, on the other hand, helps in providing guarantees at the cost of utilization. Thus need for a flexib...

Congestion control will be an essential part of B-ISDN in order to guarantee its performance level. The high transmission rate of such networks and the support of new services with diverse traffic characteristics make the congestion control problem more complicated and more challenging than in conventional networks. Voice, data and video traffic have radically different performance requirements and are of a very bursty nature. The bursty nature of the traffic is the primary cause of congestion. Congestion results in undesirable performance degradation such as long packet delay, high packet loss and large buffer requirements. Congestion control is a network function that attempts to avoid or control congestion and limit its effects. Traffic shaping has been proposed as a congestion control mechanism to control the input rate and smooth the burstiness of traffic. Shaping the traffic when it enters the network makes the traffic smoother and more predictable, thus reducing the probabilit...

Abstract ⎯ Long-range dependence (LRD) is a largely verified property of Internet traffic, which severely affects queuing performance in network buffers. A common approach for guaranteeing performance requirements is to control the statistical profile of the input traffic by regulators based on the leaky bucket scheme. In this paper, we investigate by simulation how the 1/f α power-law spectrum of LRD traffic is altered when traffic is regulated by a leaky bucket policer. Analysis of the traffic spectral characteristics is carried out mainly by means of the Modified Allan Variance, a time-domain quantity with demonstrated superior accuracy in fractional-noise parameter estimation, recently introduced also for traffic analysis. This approach allows to get a finer insight into power-law spectral characteristics of policed traffic. We also investigate some other properties of the leaky bucket fed with LRD traffic, such as its dropping probability and its effect on queuing delay in a following FIFO scheduler. Index Terms ⎯ Communication system traffic, fractional noise, Internet, long-range dependence, queuing analysis, traffic control

In networks supporting distributed multimedia, maximizing bandwidth utilization and providing performance guarantees are two incompatible goals. Heterogeneity of the multimedia sources calls for effective congestion control schemes to satisfy the diverse Quality of Service(QoS) requirements of each application. These include admission control at connection set up, traffic control at the source ends and efficient scheduling schemes at the switches. The emphasis in this paper is on traffic control at the source end. Traffic control schemes have two functional roles. One is traffic enforcement as a supplement to the admission control policy. The other is shaping the input traffic so that it becomes amenable to the scheduling mechanism at the switches for providing the required QoS guarantees. Studies on bursty sources have shown that burstiness promotes statistical multiplexing at the cost of possible congestion. Smoothing the traffic helps in providing guarantees at the cost of bandwidth...

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.