TCP-Friendly Flow Control of Wireless Multimedia Using ECN Marking

Abstract

In a wireless network, packet losses can be caused not only by network congestion but also by 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 congestion losses cannot be distinguished from wireless losses. We extend a 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 detecting congestion early, explicitly informing multimedia sources of congestion using ECN marking and calculating a TCP-friendly rate based on ECN-marked packet probability instead of packet loss probability, we are able effectively to separate the effect of wireless losses from flow control and thus prevent throughput degradation of multimedia flows traveling through wireless links. Also, we refine a 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. By simulation, we show that the proposed scheme does improve the quality of the delivered video significantly while maintaining TCP-friendliness for the case of wireless MPEG-4 video.