ITR: Design and Analysis of End-to-End Feedback Congestion Control Schemes

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The need to improve congestion control techniques for the Internet has grown recently. Non real-time data traffic, which is currently transported on a "best effort" basis, will increasingly have more stringent delay and throughput requirements to meet critical scientific, corporate and e-commerce applications. In order to meet this enhanced quality of service requirement, the existing feedback congestion control scheme incorporated in the Transmission Control Protocol (TCP) needs to be understood. For this purpose, the PIs intend to:1) Build an analytical model that can incorporate key features of TCP Reno and TCP enhancements under consideration by the IETF. The model the PIs present here is interesting in that it can accommodate multiple TCP flows and possibly multiple network nodes.2) Place TCP in a control-theoretic framework so that its stability and transient behavior is well understood. The use of non-linear control techniques proposed here is novel, and should make available a new set of mathematical tools to study this problem.3) The synthesis of these two activities will in turn suggest methods that ensure that any proposed TCP successor is stable, as well as improving throughput and fairness. A more limited goal but with perhaps more immediate impact is a better understanding of the stability and performance of TCP Reno.All of this work will be performed within the complementary congestion control efforts underway such as traffic engineering using the Multiprotocol Label Switching (MPLS) protocol, traffic shaping and policing, service scheduling and buffer management.In addition to a survey of the state of the art, the PIs present some preliminary results and ideas for future research. The PIs demonstrate an analytical model of TCP Reno for the single node case, and some of the insights that even such a simple model provides. The PIs also present a way of extending recent control theoretic work in flow control to a more realistic and general context, where boundary effects and unknown, time-varying propagation delays appear in networks. Lyapunov theory, the theory of functional (retarded) differential equations and constructive design methods in modern nonlinear control will play a key role in the synthesis of new feedback congestion control schemes for the Internet.The broader impacts of this research include the development of closer interaction between the control theory and networks research communities, curriculum enhancement at the graduate and undergraduate levels, applying some of the practical implications of this work through ongoing industry interactions, and inputs to IETF groups.