Measured analysis of TCP behavior across multihop wireless and wired networks

Emerging wireless ad-hoc networks find their most important applications in untethered, mobile, multihop scenarios where there is no wired infrastructure. Yet, when the wired infrastructure (say, the Internet) is within reach, opportunistic connections to Internet sites may be established across the multihop network to transfer files and update databases. These file transfers use TCP for reliability and congestion control. Many believe that TCP should not be used in ad-hoc network due to it´s inability to adapt to the high loss environment, but we believe that TCP will always have a part to play in wireless network in one form or another; studying the behavior of TCP will provide the direction for that adaptation. Recent experiments with ad-hoc, multihop 802.11 networks have exposed serious instabilities when TCP connections span both wired and wireless domains. In particular, some TCP connections capture the wireless channel and drive the throughput on other connections virtually to zero. This is most surprising in view of the fact that connections between 802.11 (single hop) wireless LAN stations and the Internet are well behaved, stable and fair. The problem of the unfairness compounds further when TCP connections have to share the bandwidth with in multihop ad-hoc network. In this paper, we present the issues regarding the wireless transport protocols by experimentally analyzing TCP performance.