Tcp Network Congestion Control

Internet is a packet-switched network .It is prone to congestion since neither the number of users nor their workloads are limited. In the past years , a number of congestion control schemes have been proposed .Today, the congestion control used in Internet consists of two implementations :end point algorithm and link algorithm .Both of them are studied in the thesis .TCP congestion control is the primary congestion control mechanisms used in nowadays Internet. Deeply studying TCP congestion control can not only improve the efficiency of network but also provide the reference and standard to other congestion control mechanisms. In this thesis, we study the basic algorithm of TCP congestion control including slow start ,congestion avoidance, fast recovery and fast retransmit ,and then we introduce the congestion control schemes of TCP Tahoe, Reno, New Reno and Sack.With the development of Internet, more and more mobile applications such as wireless network, GPRS, 3G are applied. To fulfill their demands for communication, some algorithms of TCP work worse. These applications can bring the problem of congestion collapse. To solve this problem, many TCP congestion control mechanisms are proposed.For wired-wireless network, we introduce a new protocol. In this paper, we have proposed a new TCP scheme called TCP-N, to improve the TCP performance in the heterogeneous network consisting of wired and wireless links. TCP-N adopts the rate-based congestion control methodology, and employs the ABE at the sender side to optimize the congestion window size when network congestion is detected. TCP-N detects the congestion by means of the CW mechanism implemented at the router that marks all packets when the router's buffer occupancy exceeds a threshold. A lot of simulations were got in NS. They verified our improvement.TCP-N improves the network in throughput, fairness and so on.