Available Bit Rate Flow Control Research Articles

Binary ABR flow control over ATM networks with uncertainty using discrete-time variable structure controller

A binary available bit rate (ABR) scheme based on discrete-time variable structure control (DVSC) theory is proposed to solve the problem of asynchronous transfer mode (ATM) networks congestion in this paper. A discrete-time system model with uncertainty is introduced to depict the time-varying ATM networks. Based on the system model, an asymptotically stable sliding surface is designed by linear matrix inequality (LMI). In addition, a novel discrete-time reaching law that can obviously reduce chatter is also put forward. The proposed discrete-time variable structure controller can effectively constrain the oscillation of allowed cell rate (ACR) and the queue length in a router. Moreover, the controller is self-adaptive against the uncertainty in the system. Simulations are done in different scenarios. The results demonstrate that the controller has better stability and robustness than the traditional binary flow controller, so it is good for adequately exerting the simplicity of binary flow control mechanisms.

Modelling and Stability Analysis of Binary ABR Flow Control in ATM Network

Available Bit Rate (ABR) flow control is an effective measure in ATM network congestion control. In large scale and high-speed network, the simplicity of algorithm is crucial to optimize the switch performance. Although the binary flow control is very simple, the queue length and allowed cell rate (ACR) controlled by the standard EFCI algorithm oscillate with great amplitude, which has negative impact on the performance, so its applicability was doubted, and then the explicit rate feedback mechanism was introduced and explored. In this study, the model of binary flow control is built based on the fluid flow theory, and its correctness is validated by simulation experiments. The linear model describing the source end system how to regulate the cell rate is obtained through local linearization method. Then, we evaluate and analyze the standard EFCI algorithm using the describing function approach, which is well-developed in nonlinear control theory. The conclusion is that queue and ACR oscillations are caused by the inappropriate nonlinear control rule originated from intuition, but not intrinsic attribute of the binary flow control mechanism. The simulation experiments validate our analysis and conclusion. Finally, the new scheme about parameter settings is put forward to remedy the weakness existed in the standard EFCI switches without any change on the hardware architecture. The numerical results demonstrate that the new scheme is effective and fruitful.

Modeling and Simulation of an ABR Flow Control Algorithm Using a Virtual Source/Virtual Destination Switch

The Available Bit Rate (ABR) service class of Asynchronous Transfer Mode networks uses a feedback control mechanism to adapt to varying link capacities. The Virtual Source/Virtual Destination (VS/VD) technique offers the possibility to segment the otherwise end-to-end ABR control loop into separate loops. The improved feedback delay and the control of ABR traffic inside closed segments provide a better performance for ABR connections. This article will present the use of classical linear control theory to model and develop an ABR VS/VD flow control algorithm. Discrete event simulations are used to analyze the behavior of the algorithm with respect to transient behavior and correctness of the control model. Linear control theory offers the means to derive correct choices of parameters and to assess performance issues, like stability of the system, during the design phase. The performance goals are a high link utilization, fair bandwidth distribution, and robust operation in various environments, which are verified by discrete event simulations. The major contribution of this work is the use of analytic methods (linear control theory) to model and design an ABR flow control algorithm tailored for the special layout of a VS/VD switch, and the use of simulation techniques to verify the result.

Relationship between the buffer threshold and the link utilization in ABR services

Rate-based flow controls play an important role in traffic management of Available Bit Rate (ABR) services. The performance of a rate-based ABR flow control is investigated. In a steady state the evolution of both the Allowed Cell Rate (ACR) and the length of queue within a switch is classified into three cases as the number of active sources varies. In each case, both the link utilization and the maximum queue length are derived. Then, for a given buffer threshold, we determine both the link utilization and the buffer size achieving zero cell loss. Numerical results show the effect of the threshold on the buffer size and the link utilization.

A simple, scalable and provably stable explicit rate computation scheme for flow control in communication networks

AbstractThis paper describes fast rate computation (FASTRAC), an explicit rate flow control algorithm for available bit rate (ABR) traffic. Using digital control theory, we develop a simple rate controller for the ABR flow control process. We prove that the controller is stable, fair to all participating sources and configurable with respect to responsiveness. The analysis presented shows that stability of the flow control process depends primarily on two factors, the control update rate and the feedback delay. The implementation of the proposed algorithm is much simpler than other fair rate allocation algorithms. The proposed algorithm demonstrates the ability to scale with speed, distance, different feedback delays, number of users, and number of nodes while remaining robust, efficient, and fair under stressing and dynamic traffic conditions. Copyright © 2001 John Wiley & Sons, Ltd.

Generalized max-min rate allocation: Theory and a simple implementation

An important concept in the available bit rate (ABR) service model is the minimum cell rate (MCR) guarantee as well as the peak cell rate (PCR) constraint for each flow. Due to the MCR and PCR requirements, the well-known max-min rate allocation policy no longer suffices to determine the rate allocation for each flow since it does not support either MCR or PCR. In this paper, we present a generalized max-min (GMM) rate allocation policy, which supports both the MCR and PCR requirements for each flow. Furthermore, a simple distributed algorithm using the ABR flow control protocol is developed to achieve the GMM rate allocation in a distributed network environment. The effectiveness of this distributed algorithm is demonstrated by simulation results.

Design and evaluation of feedback consolidation for ABR point-to-multipoint connections in ATM networks

The available bit rate (ABR) service is proposed to transport data traffic in asynchronous transfer mode (ATM) networks. ABR is unique because the network switches can indicate to the sources the rates at which they should be transmitting, thereby avoiding congestion and efficiently utilizing network resources. A number of algorithms have been developed for extending the ABR flow control algorithms for point-to-multipoint connections. In this case, feedback consolidation is required at the branch points to avoid overwhelming the sender with feedback. This paper discusses various design options and implementation alternatives for consolidation algorithms, and proposes a number of novel algorithms. The performance of the proposed algorithms and the original algorithms is compared under a variety of conditions. Results indicate that the algorithms we propose eliminate the consolidation noise (caused if the feedback is returned before all branches respond), while exhibiting a fast transient response.

Shaping Aggregate LAN Flows for Transmission over ABR Connections

AbstractIn the current recommendations on Internetworking over Non Broadcasting Medium Access and Multi‐Protocol Over ATM, the issues of ATM bandwidth allocation and flow control for best effort external LAN flows, forwarded to ATM connections, have not been adequately addressed. In this paper, we integrate the above features in the Access Units (i.e., bridges and routers) to smooth the bursty aggregate LAN traffic, to minimize losses due to congestion and consequently to achieve high end‐to‐end performance. The proposed flow control mechanism is based on the knowledge of the bandwidth available in the backbone network. Bandwidth advertising and explicit congestion notification mechanisms are provided by several network technologies such as Frame Relay and ATM. In the latter case the corresponding transfer capability is the Available Bit Rate (ABR). The proposed flow control mechanism, counts the frame delay in the Access Unit, and sends explicit feedback (backpressure) to neighboring legacy LAN sources. Explicit feedback partially absorbs the self‐similar features of the LAN traffic and can extend the ABR flow control to the non‐ATM legacy LAN stations. The shaping performed by the AU can be considered independent to the specific bandwidth advertising mechanism of the backbone network; in our case the ABR. In the performance results, the mechanism is shown to be efficient and adaptive to changes in the ATM available bandwidth and to a variety of LAN traffic characteristics. It is also shown that the flow control mechanism can be easily integrated in the protocol stacks currently met by today's LANs.

Performance of TCP traffic and ABR congestion control mechanisms

This paper presents a performance investigation of TCP traffic carried over ATM networks when the available bit rate (ABR) congestion control mechanism is exercised at the ATM layer. Two ABR schemes are investigated; the EFCI marking scheme and the relative rate marking scheme. The joint effect of the ABR mechanism with the early packet discard (EPD) mechanism is also considered. The focus of this study is to evaluate these schemes based on the effective throughput experienced by end users, taking the effect of retransmissions into account. Simulation results are obtained for a multihop switch configuration. Various aspects regarding the synergy of the TCP and ABR flow control mechanisms are presented.

ABR Flow Control for Multipoint Connections

Multipoint capabilities are essential for ATM networks to efficiently support many applications, including IP multicasting and overlay applications. The current signaling and routing specifications for ATM define point-to-multipoint capabilities. Multipoint-to-point connection support is also being discussed by the signaling and PNNI groups, and will be defined in the near future for the unspecified bit rate (UBR) service. We examine point-to-multipoint and multipoint-to-point flow control for the available bit rate (ABR) service, as discussed in the traffic management working group.

Rate based flow control with bandwidth information

AbstractThe ATM Forum has chosen the rate‐based approach for flow control of ABR (Available Bit Rate) traffic in ATM. It is based on a reactive approach whereby the transmission rate of ABR sources can be adapted to the available bandwidth at a bottleneck link. The ATM forum has specified the behavior of the source and destination, as well as the manner in which feedback information (on the available bandwidth and on the congestion state of the network) should be conveyed back to the source. The decision on the precise control mechanism, however, has been left to the designer of the switches. We propose in this paper a reactive control scheme that is based only on information on the available bandwidth. We analyze its stability, and then test its performance and fairness by simulations in the presence of other higher priority CBR or VBR traffic.