A two-phase TCP congestion control for reducing bias over heterogeneous networks

This paper presents a sender side TCP congestion control scheme that reduces biases in wired as well as wireless networks. TCP has a problem utilizing the full bandwidth in high speed networks with a long delay. Moreover, competing flows with different roundtrip times share the bandwidth unfairly; a flow with long RTT experiences a throughput penalty. The throughput penalty is severe in wireless networks since TCP treats packet losses caused by link error as an indication of network congestions that trigger transfer rate reductions. The proposed scheme controls the network congestion in two phases - a fair convergence phase and a congestion avoidance phase - both of which are based on the application's transfer data patterns. The transfer rate is then adjusted adaptively by considering the current transfer rate and the estimated bandwidth in order to reduce bias and throughputs. The scheme has been implemented in the Linux platform and experimented with various TCP variants in real environments. The experimental results show that the mechanism reduces biases, and the network bandwidth is shared fairly among the proposed and the traditional TCP flows.