Decoupling congestion control from TCP for multi-hop wireless networks

TCP performs poorly in multihop wireless networks and even worse if end-to-end connectivity is often broken such as in challenged networks. Lots of research has been carried out but this problem has not been solved completely. Recently, hop-by-hop congestion control originally proposed for wired networks has been applied for multihop wireless networks to significantly improve performances. We think that (i) moving congestion control down to lower layers is essential to overcome TCP problems in multihop wireless networks and (ii) in this case, it is necessary to further decouple congestion control from TCP. Such TCP only retains reliability control and is called semi-TCP henceforth. Due to using hop-by-hop congestion control, the congestion control efficiency of semi-TCP will not rely on the availability of end-to-end connectivity, which makes semi-TCP more suitable than TCP for challenged networks. Besides performance improvement, semi-TCP may further reduce overall system complexity by removing redundant congestion control and using simple congestion control rather than TCP congestion window. This paper discusses such a semi-TCP using a hop-by-hop congestion control that only slightly modifies the RTS/CTS protocol used in the IEEE 802.11 DCF. Furthermore, a solution to a deadlock problem in the RTS/CTS-based hop-by-hop congestion control is also studied. The performance of this semi-TCP is investigated in comparison with TCP-NewReno via simulation in NS2.