TCP Westwood: congestion window control using bandwidth estimation

Abstract

We study the performance of TCP Westwood (TCPW), a new TCP protocol with a sender-side modification of the window congestion control scheme. TCP Westwood controls the window using end-to-end rate estimation in a way that is totally transparent to routers and to the destination. Thus, it is compatible with any network and TCP implementation. The key innovative idea is to continuously estimate, at the TCP sender, the packet rate of the connection by monitoring the ACK reception rate. The estimated connection rate is then used to compute congestion window and slow start threshold settings after a congestion episode. Resetting the window to match available bandwidth makes TCPW more robust to sporadic losses due to wireless channel problems. These often cause conventional TCP to overreact, leading to unnecessary window reduction. Experimental studies of TCPW show significant improvements in throughput performance over Reno and SACK, particularly in mixed wired/wireless networks over high-speed links. The contributions of this paper include a model for fair and friendly sharing of the bottleneck link and a Markov Chain performance model in presence of link errors/loss. TCPW performance is compared to that of TCP Reno, and analytic results are validated against simulation results. Internet and laboratory measurements using a Linux TCPW implementation are also reported, providing further evidence of the gains achievable via TCPW.

Sender- Side TCP Modifications: An Analytical Study

“…These observations, together with the desire to keep the congestion control algorithm in end-hosts only, without requiring the cooperation of the network, lead to propose new versions of TCP, like Vegas [2] or Westwood [11], that try to estimate the available bandwidth (or fair bandwidth share) within the network. In both schemes the major problem arises from the difficulty of correctly estimating the available bandwidth.…”

An Optimized TCP for Internet Access of Vehicular Ad Hoc Networks

“…With the help of this information, the congestion control algorithms of TCP are modied to react accordingly depending on the predicted situation. Several approaches like TCP Westwood [ 6] try to estimate the available bandwidth in an intelligent way, which is used to optimize the TCP ow control. Other approaches like TCP DOOR [7] modify the congestion control based on the arrival of out-of-order packets, or they even examine inter-packet arrival times for using a rate-based congestion control mechanism (e.g., Wireless TCP [ 8]).…”

An enhanced TCP congestion avoidance scheme and its performance evaluation in high speed satellite networks

“…According to different message feedback mechanisms, these enhanced TCP protocols can be categorized into implicit feedback protocols, such as Scalable TCP (STCP) [3], FAST AQM Scalable TCP (FAST TCP) [4], and explicit feedback protocols, such as eXplicit Control Protocol (XCP) [5], and Variable-structure congestion Control Protocol (VCP) [6]. The Westwood protocol is another TCP enhanced protocol based on bandwidth estimation information [7]. On the other hand, protocols considering high BERs have also been proposed.…”