Do we need two forms of feedback in the Rate Control Protocol (RCP)

There is considerable interest in the networking community in explicit congestion control as it may allow the design of a fair, stable, low loss, low delay, and high utilization network. The Rate Control Protocol (RCP) is an example of such a congestion control protocol. The current design of RCP suggests that it should employ two forms of feedback; i.e. rate mismatch and queue size, in order to manage its flow control algorithms. An outstanding design question in RCP is whether the presence of queue size feedback is useful, given the presence of feedback based on rate mismatch. To address this question, we conduct analysis (stability and Hopf bifurcation) and packet-level simulations. The analytical results reveal that the presence of queue size feedback in the protocol specification may induce a sub-critical Hopf bifurcation, which can lead to undesirable system behavior. The analysis is corroborated by numerical computations and some packet-level simulations. Based on our work, the suggestion for RCP is to only include feedback based on rate mismatch in the design of the protocol.