The Weak Convergence of TCP Bandwidth Sharing

TL;DR

This paper demonstrates through theory and experiments that TCP bandwidth sharing does not converge to equal rates but instead fluctuates persistently over long periods, challenging common interpretations of TCP fairness.

Contribution

The paper provides a theoretical and experimental analysis showing TCP bandwidth sharing does not converge, revealing persistent fluctuations rather than equal sharing.

Findings

TCP flow rates fluctuate over a range close to one order of magnitude

Rate fluctuations are correlated over long intervals

Carried data volume converges slowly despite fairness

Abstract

TCP is the dominating transmission protocol in the Internet since decades. It proved its flexibility to adapt to unknown and changing network conditions. A distinguished TCP feature is the comparably fair resource sharing. Unfortunately, this abstract fairness is frequently misinterpreted as convergence towards equal sharing rates. In this paper we show in theory as well as in experiment that TCP rate convergence does not exist. Instead, the individual TCP flow rate is persistently fluctuating over a range close to one order of magnitude. The fluctuations are not short term but correlated over long intervals, so that the carried data volume converges rather slowly. The weak convergence does not negate fairness in general. Nevertheless, a particular transmission operation could deviate considerably.