TCP and network coding equilibrium and dynamic properties

This paper analyzes the impact on the TCP-Reno congestion control mechanism of a network coding (NC) layer inserted in the TCP/IP stack. A multi-source multi-link model is considered to study the equilibrium and dynamic properties of the TCP-NC protocol with RED as active queue management mechanism. The existence and uniqueness of some network equilibrium is demonstrated and characterized in terms of average throughput, loss rate, and queue length. Global stability is proved in absence of forward delay, and the effects of the NC redundancy factor and of the delay on the local stability of TCP-NC-RED is studied around the equilibrium point. Results provided by the proposed model are compared to those obtained by simulation for N sources sharing a single link. TCP-NC-RED becomes unstable when delay or capacity increases, as TCP-Reno does. Its stability region is characterized as a function of the redundancy factor.