Making TCP/NC Adjustable to Time Varying Loss Rates

Applying network coding (NC) into the protocol stack has been studied with much attention in order to improve Transmission Control Protocol (TCP) goodput in inherently lossy networks (e.g., wireless networks in unstable environments). TCP with network coding (TCP/NC) is expected to recover the lost packets without retransmission at the sink by sending the redundant combination packets which are encoded at the source. While TCP/NC can work in theory, two problems have not been well solved especially in time-varying packet loss conditions. One is how to decide the good parameters (e.g., redundancy factor R) based on a recent network condition estimated from continuous observation. The other one is how to dynamically adapt an ongoing NC-layer process based on the decided parameters. Therefore, in this paper, we propose a functionally improved TCP/NC variant called the TCP/NC with loss rate estimation (TCP/NCwLRE) which can automatically adjust the NC-layer behaviors to adapt to time-varying channels. We implemented and validated our proposal in Network Simulator 3. The results show that the TCP/NCwLRE improves the TCP goodputs in time-varying non-correlated random loss channels.