Issues in Model-Based Flow Control

This report examines potential stability problems associated with a model based apporach to TCP-friendly ow control for non-TCP traac. In speciic, such an approach involves using a TCP-friendly formula that estimates the throughput of a TCP session with the same end-to-end traac characteristics as the non-TCP connection under consideration. The inputs to this formula include the round trip time, the timeout value, and the packet loss fraction of the connection. This paper shows that estimating the loss fraction per transmitted packet highly depends on the current transmission rate of the connection as well as the actual loss fraction of the path. Thus the estimated loss fraction can contain errors which result in inaccurate estimation of the corresponding TCP throughput. This inaccuracy can push the transmission rate of the non-TCP connection away from the fair share of the bottleneck bandwidth on the end-to-end path, so that under steady state, the connection ends up receiving either over-allocation or under-allocation of bandwidth.