Novel delayed ACK techniques for improving TCP performance in multihop wireless networks

Eitan Altman

INRIA Sophia Antipolis


We study in this talk TCP performance over a static multihop network that uses IEEE 802.11 protocol for access. For such networks it has been shown in [1] that TCP performance is mainly determined by the hidden terminal effects (and not by drop probabilities at buffers) which limits the number of packets that can be transmitted simultaneously in the network. Two techniques have been proposed in [1] to improve the performance, one based on RED type technique and the other on adaptive spacing at the link layer. In this paper we propose new approaches for improving the performance based on thinning the ACK streams that competes over the same radio resources as the TCP packets. In particular, we propose a new delayed ACK scheme in which the delay coefficient varies with the sequence number of the TCP packet. Through simulations in ns, we show that the ACK thinning allows to increase TCP throughput by around 50, which is substantially more than the previous improvement methods.

Ref: [1] Z. Fu, P. Zerfos, H. Luo, S. Lu, L. Zhang, M. Gerla, ``The impact of multihop wireless channel on TCP throughput and loss'', to appear in IEEE INFOCOM 2003. Available on

This is a joint work with T. Jimenez

[Eitan Altman]
[INRIA Sophia Antipolis]