Transmission Control Protocol (TCP) is known to suffer from performance degradation in mobile wireless environments. This is because such environments are prone to packet losses due to high bit error rates and mobility induced disconnections. TCP interprets packet losses as. an indication of congestion and inappropriately invokes congestion control mechanisms, which leads to degraded performance. In this paper we show how cross-layer feedback, i.e. information from layers above and below, may be used to improve TCP performance over wireless networks. To illustrate the power of cross layer feedback, we present two novel mechanisms. One, we incorporate user feedback into the protocol stack by which the TCP throughput of a desired set of applications running on the mobile host can be dynamically controlled. Other, we propose an approach to use the lower layer connection and disconnection information, for improving TCP performance. Both these mechanisms entail minimal modification to the mobile host and no modifications to the sender or other network entities. We have implemented both these mechanisms in ns-2 and the simulation results demonstrate the effectiveness of cross layer feedback.
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