Proxy-based TCP-friendly streaming over mobile networks

Mobile media streaming is envisioned to become an important service over packet-switched 2.5G and 3G wireless networks. At the same time, TCP-friendly rate-adaptation behavior for streaming will become an important IETF requirement. In this paper we investigate TCP-friendly on-demand streaming over wired and wireless links. We consider two approaches for achieving TCP-friendliness: first, by tunneling RTP packets over TCP and secondly by employing an RTP server rate control which does not exceed a variable rate constraint derived from the recently developed TFRC protocol. To allow a reasonable fair comparison between TCP and TFRC, we assume a simple retransmission mechanism on top of TFRC. We consider streaming from a server in the public Internet to both wired and wireless clients. For the wireless case we assumed a client which is connected to the public Internet via a dedicated 64 kbps WCDMA streaming bearer. Simulation results carried out in ns-2 show that TCP and TFRC can not fully utilize the WCDMA bearer at 5% packet loss rate over the shared public Internet link. Smooth playout of a typical 64 kbps video stream would require high initial buffering delays (>10 seconds) and large receiver buffer sizes (>60 KB). We finally investigate the gains from a proxy that splits the connection and uses TCP-friendly congestion control only over the shared part of the client-server connection. Simulation results show improvements in average throughput and wireless link utilization. By employing appropriate packet re-scheduling mechanisms, the initial buffering delay and the client buffer size for a typical 64 kbps video stream can be decreased by a factor of three to four.