TCP-friendly wireless multimedia flow control using ECN marking

In a wireless network packet losses can be caused by not only network congestion but also unreliable error-prone wireless links. Therefore, flow control schemes which use packet loss as a congestion measure cannot be directly applicable to a wireless network because there is no way to distinguish congestion losses from wireless losses. In this paper, we extend so-called TCP-friendly flow control scheme, which was developed for the control of multimedia flows carried over UDP in the presence of TCP flows, to a wireless environment by using ECN (Explicit Congestion Notification) marking capability with RED (Random Early Detection) routers. By early detecting congestion, explicitly informing multimedia sources of congestion using ECN marking and calculating TCP-friendly rate based on ECN-marked packet probability instead of packet loss probability, we were able to effectively separate the effect of wireless losses from flow control and thus prevent throughput degradation of multimedia flows traveling through wireless links. In addition, we refine well-known TCP throughput model developed for TCP-friendliness of multimedia flows such that the refined model provides more accurate estimate of TCP flows' throughput when both ECN marking and RED queue management are used. Through simulations we show that the proposed scheme indeed improves the quality of delivered video significantly while maintaining TCP-friendliness for the case of wireless MPEG-4 video.