Performance evaluation and comparison of TCP algorithms in static multihop wireless networks

Wireless ad hoc networks are characterized by multihop wireless connectivity and limited bandwidth shared among neighbouring nodes. In this paper, we investigate and evaluate the performance of TCP NewReno, TCP SACK and TCP Vegas in this kind of network over AODV routing protocol and the wireless LAN standard IEEE 802.11 MAC layer. The performance of these TCP variants is compared on the basis of several performance measures that include throughput, retransmission ratio, average congestion window size and routing overhead. Simulation results using ns-2.28 show that TCP Vegas achieves between 15% and 130% more throughput, around 99% less packet retransmissions and around 93% less routing overhead than TCP NewReno and TCP SACK. The paper gives insight on the particular reasons for such performance advantages of TCP Vegas in comparison to TCP NewReno and TCP SACK. Furthermore, we investigate the performance of these TCP algorithms when they are run with the Delayed Acknowledgment (DA) option defined in IETF RFC 1122, which allows the TCP receiver to transmit an ACK for every two incoming packets. Simulation results show that use of DA option substantially improves the performance for TCP NewReno and TCP SACK. It also results in performance improvement for TCP Vegas but as not as much as that of TCP NewReno and for longer hop connections, it can even cause throughput degradation of Vegas. We also observed the effect of TCP packet size on the throughput and packet delivery ratio of TCP NewReno and Vegas. Simulation results show that an increase in packet size reduces the fraction of packets delivered successfully. Increasing the packet size increases the throughput till a certain threshold and there is a decrease in throughput after the threshold.