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Abstract : |
Congestion and flow control is an integral part of any Internet data transport protocol. It is widely accepted that the congestion avoidance mechanisms of TCP have been one of the key contributors to the success of the Internet. However, TCP is ill-suited to real-time multimedia streaming applications. Its bursty transmission, and abrupt and frequent wide rate fluctuations cause high delay jitters and sudden quality degradation of multimedia applications. For asymmetric networks such as wireless networks, cable modems, ADSL, and satellite networks, transmitting feedback for (almost) every packet received as it is done in TCP causes congestion in the reverse path. In this environment, TCP may severely underutilize the forward path throughput. Use of multicast further complicates the problem; TCP-like frequent feedback from each receiver to the sender in a large scale multicast session cause well-known scalability limitations (e.g. acknowledgment implosion). We have developed a new flow control approach for multimedia streaming, called TCP emulation at receivers (TEAR). TEAR shifts most of flow control mechanisms to receivers. In TEAR, a receiver does not send to the sender the congestion signals detected in its forward path but rather processes them immediately to determine its own appropriate receiving rate. TEAR can determine this rate using congestion, |
