CONTENTION AWARE CROSS LAYER OPTIMIZATION OF TCP IN MANETS

Abstract

Numerous studies and modifications have been done for the performance enhancement of Transmission Control Protocol (TCP) in mobile ad-hoc networks. Because TCP was initially designed basically for wired networks. Any type of packet drop is treated as congestion nearly by all the TCP variants. IEEE 802.11 is the underlying protocol for accessing the wireless channel. It is a channel reservation mechanism based on contention. A number of studies have revealed that the reason behind poor performance of TCP in ad-hoc networks is the incompatibility or lack of coordination between MAC and TCP layer. This research focuses on the joint coordination of TCP and MAC layer i.e. the proposed Contention Aware Cross TCP (CAC-TCP). The congestion call invoked due to MAC layer contention are avoided by the proposed algorithm and are dealt accordingly. A threshold has been set at the MAC layer for measuring the level of contention. If the threshold is reached the event is notified to TCP to slow down the sending rate according to the mechanism defined in CAC-TCP. The standard congestion control algorithm is not invoked in response to the packet lost due to contention due to awareness of distinguishing between contention and congestion losses. The implementation of the proposed CAC-TCP is done in the NS-2 environment. The simulation results revealed that performance of proposed CAC-TCP is much higher than TCP throughout the simulation. A significant improvement has been showed by the proposed solution by showing an increase of 14.2% in terms of throughput while a reduction of 7.8 % has been recorded in drops while keeping the delay low making an improvement of 1.6 %.