On the Design of Interfaces for Tcp/ip over Wireless

Supporting data applications over networks comprising both wireless and wireline links is of increasing importance for both military and commercial systems. Many standard data applications on current wireline networks are based on TCP/IP, the end-to-end ow and congestion control protocol widely used on the Internet, so that it is of crucial importance to devise network level controls that enable TCP to perform well when the path from source to destination includes one or more wireless links. Since TCP has been recently shown to perform poorly in the presence of random loss, its performance over a lossy wireless link subject to deep fades and other impairments may be unsatisfactory. In this paper, we show that a suitable link level error recovery mechanism can \hide" the uctuations of the wireless medium from TCP, and we provide an analytical framework for predicting TCP performance as a function of the wireless channel characteristics and the size of the wireless-wireline interface buuer. The analytical predictions are validated by simulations, and show that the size of the buuer required is moderate in comparison with the buuer size already required to provide good performance using TCP in a wireline network. This is consistent with an asymptotic argument that implies that the size of the interface buuer required to deal with channel time variations grows logarithmically with the bandwidth-delay product, while the size of the buuer required to achieve high utilization using TCP in a wireline network grows linearly with the bandwidth-delay product.