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 andan outer loop. The inner loop works on a per-packet time scale, and is governed by the so calledack-clock. The outer loop adjusts the sending win-dow based on an estimate of the network state. Inthis paper, we analyze the behaviour of the innerloop in a bottleneck topology with constant crosstraffic. It is shown that the inner loop is globallyasymptotically stable and that the time constantfor local convergence is smaller than four times theroundtrip time. These results are applied to the de-sign of a new outer loop control mechanism for mo-bile terminal download. Information on radio band-width and queue length available in the radio net-work controller (rnc), close to the base station, isused in a proxy that resides between the Internetand the cellular system. The control algorithm inthe proxy is window-based and sets the window sizeaccording to event-triggered information on radiobandwidth changes and time-triggered informationon the queue length of the rnc. The properties ofthis control scheme is analysed.