Robust Explicit Congestion Controller Design for High Bandwidth-Delay Product Network: A H∞ Approach

TCP becomes inefficient and prone to instability when its bandwidth-delay product increases. By sending explicit congestion information from routers to end hosts, both XCP and API-RCP have been proposed to solve the stability issue of TCP in high bandwidth-delay product networks. Since the estimation errors of the network parameters are unavoidable, we would like to design a robust controller to address this type of model uncertainty in the explicit congestion control system. We employ the H_∞ optimal criterion in our design, and select a proper weight function to solve the H_∞ sensitivity problem. By using the maximum modulus theorem from the robust control theory, we obtain an optimal internal model controller from which a robust H_∞ controller can be derived. OPNET simulations demonstrate that our H_∞ controller exhibits a good robustness to varying network parameters. Performance comparison between our robust explicit congestion controller and TCP/RED is provided.