Equation-Based Rate Control: Is it TCP-Friendly?

TCP-friendliness is an axiom that requires packet sources in the Internet to attain a long-run time-average send rate that is not larger than TCP would achieve. We consider equation-based rate control, with TCP-friendliness as one design goal. We suggest to breakdown the TCP-friendliness condition into sub-conditions and study them separately. There are four sub-conditions whose conjuction implies TCP-friendliness. One such sub-condition is conservativeness; it means that a source verifies the throughput formula with respect to the average send rate, loss-event rate, and average round-trip time as perceived by this source. We show an elegant analysis that yields conditions that determine either conservativeness or non-conservativeness. Another sub-condition is that the loss-event rate as observed by the source is not smaller than that of TCP. We give analysis arguments that identify scenarios when either ordering of the loss-event rates is an outcome. We identify cases when an equation-based rate control can experience a dramatically smaller loss-event rate than TCP, and this ultimately results in a gross non-TCP-friendliness. We complement our analysis with experimental results, including simulations and Internet measurements. We argue that the TCP-friendliness condition is difficult to verify. On the contrary, and a more positive side, conservativeness lends itself to an elegant analysis, and moreover, it is not based on the monopoly of TCP-centric design.