Wireless TCP approaches

There are several approaches to enhancing wireless TCP [BPSK97]. The first is the Split-TCP approach, which breaks the link into a wired component and wireless component. However, this approach requires hard state, and breaks the TCP end-to-end model. Another approach is Snoop-TCP, which puts a snoop agent on the access point, intended to detect lost packets and retransmit them before the TCP endpoints notice the loss. This has the disadvantage of requireing a smart access point.

Link-layer retransmission is currently used in 802.11. This causes problems because retransmissions take priority over other traffic, and the variable RTT (round trip time) experienced by the endpoints can confuse advanced TCP implementations that use changes in RTT to estimate congestion.

A recent proposed development [LJ] called Congestion Coherence proposes client and server TCP changes to correlate losses associated with packets coming back with the ECN bit set as congestion, and losses not associated with ECN tagged packets as losses due to noise. This has the advantage of not requiring any new technology on the intervening network, however it does require that ECN be fully deployed on the links being used.