TCP-Aix : making TCP robust to reordering and delay variations

In this paper, we describe and evaluate TCP-Aix, a sender-side TCP algorithm designed to make TCP performance robust to packet reordering and delay. TCP-Aix consists of three novel components: (i) decoupling of loss recovery actions from congestion control actions, (ii) candid growth of the congestion window upon reception of dupacks, allowing for improved performance in reordering environments, and (iii) an algorithm for determining an appropriate dupthresh value. The results from our simulation study show that, by combining these three components, the performance of TCP-Aix is largely impervious even to the highest packet reordering rates investigated in this paper of 8\%, where the duration of the reordering is in the order 2-3 end-to-end RTTs. TCP-Aix outperforms a simulated state-of-the-art TCP sender as well as a TCP-NCR sender, the performance of which both display a much stronger dependence on packet reordering. Improved performance in the presence of delay spikes is also shown. Strengthened by simulation results, we further argue that the improved performance of TCP-Aix does not come at the expense of other, competing, TCP senders. Rather, the TCP-Aix senders utilise bandwidth that would otherwise have been left unutilised. We therefore believe that a gradual deployment of TCP-Aix would be feasible.Godkänd; 2006; 20070201 (ysko)