Agent-based rate coordination between TCP and ABR congestion control algorithms

In this paper we study the extent of negative interactions between Transmis sion Control Protocol (TCP) and Asynchronous Transfer Mode (ATM) congestion control through the application of an approach based on coordination via e xplicit cooperation. To do so, we implement an agent that bridges the gap b etween the ATM layer and the TCP layer in the protocol stack at the sender end to coordinate the congestion control algorithms of the TCP transport pr otocol and the ATM cell-oriented switching architecture. The novel idea use s ATM rate-based how control to adjust the credit-based window size of TCP via the implementation of the agent. The effects of running TCP over Available Bit Rate (ABR) are studied with t he help of two simulation models (LAN and WAN). Firstly, we show that TCP w indow (CWND) and ABR Actual Cell Rate (ACR) are weakly correlated. Secondly , we derive an Agent-based algorithm to ensure that even when the ATM switc h queues are indicating no congestion, it is the switch land not the source ) which should control the increment in the TCP source rates. The introduct ion of the agent at the edge of the network coordinates the TCP and ATM sen ding transmission and clearly demonstrates a strong correlation coefficient between CWND and ACR. The simulation results show that coordination at the edge of the network makes better use of available bandwidth and improves T CP's performance over ATM for a range of performance metrics such as Cell L oss Ratio, Packet Retransmission Ratio and Throughput. (C) 2001 Elsevier Sc ience B.V. All rights reserved.