Research On Congestion Control Algorithm Based On Cross-layer In Ad Hoc Networks

Resources of bandwidth is limited in wireless Ad hoc network, the transmission of burst data is too much, because of those they could cause congestion. Congestion control is an effective and fair way to solve problems between network resources and information flows. In the Internet, TCP congestion control algorithms have become important factors to ensure network stability. However, the traditional TCP congestion control algorithms are not adapt to the wire Ad hoc network because of the characteristics of the wireless Ad hoc network, and the existing TCP congestion control mechanisms can not meet the needs of wireless Ad hoc networks. Therefore, the research of wire Ad hoc network has become a hot topic based on the thought of cross-layer.Using the simulation software, NS2, the thesis analysises the congestion control of two versions, TCP Tahoe and TCP Reno, in wire network and wireless Ad hoc network and draws conclusions. Firstly, the performance of TCP congestion control is better and more difficult to loss packets. Secendly Due to packet loss often occurs in wireless Ad hoc network, throughput and performance of TCP congestion control is lower. It is because congestion is not the only reason of packet loss. To solve this problem, the thesis presents a program of cross-layer, parameters in MAC layer adjust that in transport layer in older to change the value of sending rate.The thesis snalysises the traditional rate-based congestion control algorithm and its problems, optimize sending rate in transport layer based on the thought of cross-layer. Optimizing parameters has two ways. On the one hand, optimization of parameter R,round-trip time,can be calculated through the MAC layer delay and the thesis divides the multi-hop network into a number of single-hop network. On the other hand, optimization of parameter p, packet loss, can be calculated in the sender instead of receiver because the ACK is also easy to lose. The value of p can be calculated by counting the number of repeat of ACK. The value of parameter R and p can be calculated in MAC layer and they can be transfered by information sharing based on cross-layer in older to control congestion.The thesis establishs the network models of single-hop network and multi-hop network and uses NS2to simulate. The thesis compares the delay and throughput between the improved MEBCC algorithm and original EBCC algorithm and the results show that the performance of improved MEBCC algorithm in the network transmission has been obviously improved than the original EBCC algorithm.