The Improvement Of Tcp Vegas Algorithm Based On Explicit Congestion Notification

With the evolvement of Internet based on TCP/IP, the scale, users and traffics of Internet have experienced an explosive growth since 1990's. The network congestion has become more serious and complex due to the ever-increasing network application types and dynamic network parameters such as active sessions and round trip time. Congestion often results in decline of quality of service (QoS) in terms of transmission delay and throughput, which affects the utilization of network resource like bandwidth and buffers. Therefore, it is important to solve the congestion problem effectively for improving network performance. How to avoid and control congestion is one of the most active fields in the computer networks.Traditionary congestion avoidance mechanism just starts up congestion avoidance algorithm when measures the drop of datagram, this is actually a remedial measure after network has exited congestion. But TCP Vegas controls and avoids congestion through comparing with the difference of actual throughput and anticipant throughput. TCP Vegas makes use of the ratio of congestion window and datagram Round-Trip Time to calculate the throughput of links, moreover maintains the throughput betweenαandβ. Trough reasonable adjusting congestion window size, Vegas can avoid congestion, at the same time holding a larger throughput.But in heterogynous network environments when TCP Reno and TCP Vegas both exit, TCP Reno will persists increasing congestion window size until a datagram drop has registered to indicate occurring congestion. That may results in queue delay and Round-Trip Time of TCP Vegas increasing, finally congestion window size of TCP Vegas will decrease. In this way, for avoiding unfair distribution of bandwidth, the aggression of TCP Vegas ought to increase.This paper addresses incompatibility issues between TCP Reno and TCP Vegas, so we put forward a new algorithm. Simulation results show that our new algorithm can effectively restrict TCP Reno from unfairly grabbing the bandwidth share of TCP Vegas. The followings are the main contents.