Research On Congestion Control Algorithm Of High Speed Networks

The development of computer network technology leads to the appearance of many high speed networks which bandwidth larger than lOGbps. Through high speed networks, applications like scientific collaboration, telemedicine and real time environment monitoring can transfer high bandwidth real time data, images and video captured from remote sensors such as satellites and radars. At present, while the research of congestion control of high speed networks is still in the initial stage at home and abroad, there have been some representative high speed congestion control algorithms, namely HSTCP, STCP, BIC TCP, CUBIC TCP, FAST TCP etc. These new algorithms greatly increase the performance of high speed networks by adjusting the increase and decrease mechanism of congestion window. For the simplicity and scalability of the implementation of HSTCP, it is accepted by the IETF. HSTCP can obtain very high throughput in the current high speed networks, but there still some serious performance deficiencies.First of all, on the basis of analyzing the limitations of TCP Reno applying in high speed network, several congestion control algorithms which are currently used in high speed networks and the evaluation criterion are briefly introduced. Through the establishment of OPNET simulation model, the efficiency of several high speed TCP algorithms is analyzed.Secondly, HSTCP congestion control algorithm is investigated systematically, focus on its performances and imperfect. When drop tail queue management is adopt, the flow with small RTT can obtain very large bandwidth resource and conversely the flow with large RTT can obtain very little networks resource. So HSTCP algorithm is lack of RTT fairness. When the same bandwidth is shared by HSTCP and traditional TCP and the packet loss rate is small, HSTCP will seize large number of bandwidth, resulting in very poor TCP friendliness.Finally, based on the above analysis, HSTCP algorithm is improved and a new algorithm, W-HSTCP is put forward. In the environment of high speed networks, the W-HSTCP makes some improvement about the friendliness with regular TCP Reno. It's RTT fairness is also enhanced. W-HSTCP eliminates the relation of proportion between the increasing window and RTT by adding a fairness factor. By estimating the current network bandwidth, the transfer mode between the traditional TCP and W-HSTCP is adjusted, avoiding W-HSTCP flow excessively occupies network resources and reserving more resources to traditional TCP, so as to improve the TCP friendliness. The performance test is carried out, and the simulation results show that the improved algorithm has good performance.