Abstract:

In this work, we study the behavior of TCP protocol over multihop ad-hoc networks. TCP is a reliable transport protocol that at first was conceived for wired networks. The congestion control mechanism of TCP is designed for wired environments and is not adapted with wireless networks such as multihop ad-hoc networks which have different characteristics in terms of loss. TCP congestion control mechanism is based on the fact that the main reason of loss in wired networks is the buffer overflow. This mechanism is not adapted with ad-hoc networks where the main reason of loss is link contention caused by hidden terminal problem. Through simulation, we show that TCP throughput drops significantly because it generates somewhat a "bursty" traffic that increases the contention in the MAC layer which results to collisions and packet losses. We then introduce a new approach to improve the performance of TCP. For controlling the ''aggressive'' traffic of TCP, we propose to add a shaper in order to release the packets in the network in a controlled rate. We show that using this mechanism plus the delayed ack option improves TCP throughput by more than 50% when compared to standard TCP.