TCP Westwood with adaptive bandwidth estimation to improve efficiency/friendliness tradeoffs
In this paper, we propose an extension of Transmission Control Protocol (TCP) Westwood allowing the management of the Efficiency/Friendliness-to-NewReno tradeoffs. We show that the extended TCP Westwood is able to achieve higher total link utilization, yet at the same time maintain friendliness. TCP Westwood (for short, TCPW) implements a novel window congestion control algorithm based on eligible rate estimation (RE). The performance of TCPW has been promising, exceeding that of TCP NewReno in 'large leaky pipes'; i.e. network paths with high bandwidth-delay product and non-negligible random error rate. Consider the situation where TCPW and TCP NewReno connections coexist and share common bottlenecks. Friendliness in this shared environment is paramount. Under certain conditions TCP NewReno may experience some performance degradation since TCPW 'learns' more about connection performance and thus can take better advantage of available bandwidth. To manage the efficiency/friendliness tradeoffs, we propose to combine the original TCPW Bandwidth Estimation (BE) strategy with a new RE strategy. One finds that BE provides significantly higher utilization, but may, under certain conditions, overestimates a connection fair share. RE, on the other hand, tends to be closer to the achieved rate of a connection, but it may underestimate the connection fair share. The question is: which estimate-RE or BE-yields better throughput/friendliness tradeoffs? Our studies show that RE works best when packet loss is mostly due to congestion. If, on the other hand, packet loss is mostly due to link errors, BE gives better performance. To achieve the 'best of all worlds', we introduce a method we call Combined Rate and Bandwidth estimation (CRB.) A connection first infers the predominant cause of packet loss (buffer congestion or random error) and then uses the more appropriate estimation method. Simulation shows that the adaptive CRB provides a very effective compromise between efficiency and friendliness. (C) 2003 Elsevier B.V. All rights reserved.
tcp westwood bandwidth estimation congestion control efficiency friendliness tradeoffs