Stability of window-based queue control with application to mobile terminal download

Window-based transmission control, such as tcp, is a cascaded control system with an inner and an outer loop. The inner loop works on a perpacket time scale, and is governed by the so called ack-clock. The outer loop adjusts the sending window based on an estimate of the network state. In this paper, we analyze the behaviour of the inner loop in a bottleneck topology with constant cross traffic. It is shown that the inner loop is globally asymptotically stable and that the time constant for local convergence is smaller than four times the roundtrip time. These results are applied to the design of a new outer loop control mechanism for mobile terminal download. Information on radio bandwidth and queue length available in the radio network controller (rnc), close to the base station, is used in a proxy that resides between the Internet and the cellular system. The control algorithm in the proxy is window-based and sets the window size according to event-triggered information on radio bandwidth changes and time-triggered information on the queue length of the rnc. The properties of this control scheme is analysed.