TCP Congestion Control over HSDPA: an Experimental Evaluation

TL;DR

This paper experimentally evaluates four TCP congestion control variants over HSDPA, revealing differences in round trip times, retransmissions, and delays, with Westwood+ showing the best delay performance.

Contribution

It provides a comparative analysis of TCP variants over HSDPA, highlighting their performance differences and the impact of congestion control algorithms in wireless networks.

Findings

All TCP variants achieve similar goodputs.

TCP BIC/Cubic have higher round trip times and retransmissions.

TCP Westwood+ has the shortest round trip delays.

Abstract

In this paper, we focus on the experimental evaluation of TCP over the High Speed Downlink Packet Access (HSDPA), an upgrade of UMTS that is getting worldwide deployment. Today, this is particularly important in view of the "liberalization" brought in by the Linux OS which offers several variants of TCP congestion control. In particular, we consider four TCP variants: 1) TCP NewReno, which is the only congestion control standardized by the IETF; 2) TCP BIC, that was, and 3) TCP Cubic that is the default algorithm in the Linux OS; 4) Westwood+ TCP that has been shown to be particularly effective over wireless links. Main results are that all the TCP variants provide comparable goodputs but with significant larger round trip times and number of retransmissions and timeouts in the case of TCP BIC/Cubic, which is a consequence of their more aggressive probing phases. On the other hand, TCP Westwood+ provides the shortest round trip delays, which is an effect of its unique way of setting control windows after congestion episode based on bandwidth measurements.