Performance evaluation of Transmission Control Protocol in mobile ad hoc networks

Transmission Control Protocol (TCP) is a widely accepted, reliable, end-to-end, transport layer communication protocol. It has a self generating error control mechanism to achieve reliability using error correction. It also a has flow control scheme to avoid network congestion using a window mechanism. TCP is tuned to perform well in traditional wired networks, where packet losses are primarily due to congestion. However, with the increase in wireless communication, there is an immense need of adapting TCP to the wireless environment. Packet loss in wireless networks could be due to bit error rate (BER), link failure or handoffs. If standard TCP is applied on such wireless networks without any modification, it may lead to performance degradation. To address these problems, many solutions have been proposed for TCP enhancements over wireless networks. We have analyzed the performance of New Reno, selective acknowledgements (SACK), explicit congestion notification (ECN) and Westwood by simulation. The performance was measured on the basis of average throughput, packet loss ratio and average end-to-end delay in three different situations: mobility (variable speed); link loss; both mobility and link loss. Results show that New Reno is more stable and consistent in the absence of congestion, otherwise ECN performs best.