Research On Congestion Control Scheme For TCP With Network Coding

Benefiting from wireless communication technology, it is convenient to access to the Internet ubiquitously. However, the topology and channel quality of wireless network is changing, and collisions exist among wireless nodes, which may cause packet loss. This kind of interference will effect congestion control sheme in transport protocols, leading to low throughput. Network coding is introduced into transport layer. TCP with network coding (TCP/NC) makes the packet loss, which is caused by wireless transmission error, has no effect on congestion control. TCP/NC can also reduce the delay caused by explicit retransmission notification.As a new scheme, TCP with network coding must ensure that it takes full advantage of network coding to mask wireless loss from interfering congestion control scheme, as well as do not deviate from the favorable design rules of the original scheme, such as fairness and TCP friendliness. TCP/NC must improve the throughput of TCP flow without damaging the performance of other competing flows. In this thesis, we consider TCP with network coding both in single-path and in multi-path. In single-path TCP/NC, it may not be fair when both TCP flow and TCP/NC flow coexist in wired bottleneck link in hybrid wired-wireless network, because of different perception and reactions to the same congestion level. In multipath TCP (MPTCP) with network coding, network coding invalidates the load-balancing feature in multi-path TCP congestion control schemes, which deviates the deign rules in multipath TCP. Hence, we propose two congestion control schemes for single path and multipath TCP with network coding respectively. The main contribution of this paper is as follows:1) TCP/NC is an end to end transmission technology. To employ TCP/NC in a wider area of network, especially in hybrid wired-wireless network, congestion exposure enabled TCP/NC, namely CEE-TCP/NC, is proposed to make TCP/NC be friendlier to TCP protocol and avoid damaging the performance of TCP protocol in the case of congestion. CEE-TCP/NC do not simply depend on duplicated ACK and variation of round trip time (RTT) to expose congestion. The congestion exposure scheme also depends on the characteristics of congestion loss. By theoretic analysis and simulation, it verified that this scheme not only inherits the advantage of network coding to eliminate the effect of wireless transmission error, but also takes action against packet loss caused by congestion according to different congestion level. 2) To deal with the invalidation of the load balancing feature of congestion control scheme in MPTCP with network coding. We firstly discuss this complex issue about the fairness problem. Then, a new end-to-end congestion control solution, named Couple+, is presented to deal with the unfairness among subflows. Couple+can, on the one hand, expose congestion timely and migrate load among subflows reasonably; on the other hand, keep TCP friendly to other flows in bottlenecks. By simulation, the performance analysis proves that, unfairness among subflows indeed exists and our scheme is reasonable and can balance congestion among coded and non-coded subflows, which makes network coding collaborate better with MPTCP.