Network aware applications react to changing network conditions, offering potential quality of service differentiation without network support. We describe an application level approach to designing a low priority service — one that is ‘lower than best-effort’ in the context of the Internet. Such applications are appropriate for background ﬁle transfers, such as OS updates. We use a receive window control to limit the transfer rate of the application, and the optimal rate is determined by detecting a change-point. We motivate this joint control-estimation problem by considering a ﬂuid-based optimisation framework, and describe practical solutions, based on stochastic approximation and binary search techniques. Simulation results demonstrate the effectiveness of the approach.