Controller design for TCP rate management in QoS networks

CARM is a recent rate management technique designed to provide throughput differentiation among TCP aggregates, as may be required in QoS architectures such as DiffServ Assured Forwarding Per-Hop-Behavior. In this paper we derive the system model for a TCP aggregate that is DiffServ controlled, and use it for the analytical design of the PI controller employed in CARM. The model explicitly accounts for DiffServ parameters such as the finite token bucket depth and contract rate. The designed controller leads to fast convergence and has parameters that can be locally computed. The use of integral control action can lead to the phenomenon of integral windup in realistic network scenarios, so the controller design also includes an anti-integral-windup formulation. We present ns-2 simulation results that validate our design.