On the long-run behavior of equation-based rate control

• Authors: Milan VojnoviΕ;Jean-Yves Le Boudec
• Venue: Proceedings of the 2002 conference on Applications, technologies, architectures, and protocols for computer communications
• Year: 2002

We consider unicast equation-based rate control, where a source estimates the loss event ratio $p$, and, primarily at loss events, adjusts its send rate to $f(p)$. Function $f$ is assumed to represent the loss-throughput relation that TCP would experience. When no loss occurs, the rate may also be increased according to some additional mechanism. We assume that the loss event interval estimator is non-biased. If the loss process is deterministic, the control is TCP-friendly in the long-run, i.e, the average throughput does not exceed that of TCP. If, in contrast, losses are random, it is a priori not clear whether this holds, due to the non-linearity of $f$, and a phenomenon similar to Feller's paradox. Our goal is to identify the key factors that drive whether, and how far, the control is TCP friendly (in the long run). As TCP and our source may experience different loss event intervals, we distinguish between TCP-friendliness and conservativeness (throughput does not exceed $f(p)$). We give a representation of the long term throughput, and derive that conservativeness is primarily influenced by various convexity properties of $f$, the variability of loss events, and the correlation structure of the loss process. In many cases, these factors lead to conservativeness, but we show reasonable experiments where the control is clearly non-conservative. However, our analysis also suggests that our source should experience a higher loss event ratio than TCP, which would make non-TCP friendliness less likely. Our findings provide guidelines that help understand when an equation base control is indeed TCP-friendly in the long-run, and in some cases, excessively so. The effects of round trip time and its variations are not included in this study.