TCP-friendly flow control of wireless multimedia 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 originally developed for the flow control of multimedia flows in a wired IP network environment, to a wireless environment. The main idea behind our scheme is that by using ECN (Explicit Congestion Notification) marking in conjunction with RED (Random Early Detection) queue management scheme intelligently, it is possible that not only the degree of network congestion is notified to multimedia sources explicitly in the form of ECN-marked packet probability but also wireless losses are hidden from multimedia sources. We calculate TCP-friendly rate based on ECN-marked packet probability instead of packet loss probability, thereby effectively eliminating the effect of wireless losses in flow control and thus preventing throughput degradation of multimedia flows travelling through wireless links. In addition, we refine well-known TCP throughput model which establishes TCP-friendliness of multimedia flows in a way that the refined model provides more accurate throughput estimate of a TCP flow particularly when the number of TCP flows sharing a bottleneck link increases. Through extensive simulations we show that the proposed scheme indeed improves the quality of delivered video significantly while maintaining TCP-friendliness in a wireless environment for the case of wireless MPEG-4 video. Index Terms Multimedia flow control, wireless loss, ECN marking, RED, TCP-friendliness, MPEG-4 video