Research And Improvement On Congestion Control Mechanism Of SCTP

Stream control transmission protocol is a new protocol for transport layer published in the year of 2000. Since SCTP has many innovative characteristics, it has become a universal protocol for transport layer and the hot spot of networks researches. SCTP can not detect the mild congestion and sharply reduce the throughput when it detects the loss of the datagram. This thesis is trying to deal with the two problems and proposes an improved SCTP Vegas congestion control mechanism. The aim is to detect the network congestion earlier and to take steps to avoid the loss of the datagram. It mainly modifies the algorithm of slow start, the algorithm of congestion avoidance and the algorithm of fast retransmit. The algorithm of slow start adopts different increase strategy of congestion window by comparing the congestion window and slow start threshold. The algorithm of congestion avoidance alters congestion window by the comparison of the throughput. The algorithm of fast retransmit may work when SCTP receives a duplication of acknowledgement.This thesis mainly analyses the main characteristics of SCTP and compares with the characteristics of tranmission control protocol(TCP) and user datagram protocol(UDP). It analyses the congestion control mechanism of TCP Reno,SCTP and TCP Vegas. It draws lessons from the core ideology of TCP Vegas congestion control mechanism and proposes an improved SCTP Vegas congestion control mechanism. It mainly modifies the algorithm of slow start, the algorithm of congestion avoidance and the algorithm of fast retransmit. It models and analyses the performance when SCTP and TCP Reno share the bandwidth. It is apply to the applications traditionally supported by TCP in theory. It simulates the new mechanism based on the level of the programming of C++ and OTcl on the platform of NS2, modifeies the source codes of NS2.28 to implement the new mechanism. It validates the characteristics of multihoming and multistreaming. It sets up the environment of the limited bandwidth with inaccurate model, simulates the new mechanism and analyses the quotas of quality of service such as delay,jitter and drop rate. The results show SCTP Vegas congestion control mechanism is better than SCTP on the quotas of delay and drop rate and they differ seldom on the quota of jitter.