Modeling TCP performance over wireless channels with a semi-reliable data link layer

Providing reliable data communications over wireless channels is a challenging task due to the time-varying wireless channel characteristics that often lead to bit errors. These errors propagate to the higher layers, causing loss of protocol data units. ARQ and FEC try to prevent this, providing a reliable service to the higher layers. Most analytical models that studied the effect of ARQ and FEC assumed that the ARQ scheme is fully reliable, meaning that a frame is successfully transmitted irrespective of the amount of retransmission attempts it takes. In this paper, we study the effect of a semi-reliable data link layer on performance experienced by TCP. We develop an analytical model for a TCP SACK connection running over a wireless channel with a semi-reliable ARQ, where the amount of retransmission attempts is limited by some number. The model allows to evaluate the effect of many parameters of wireless channels on TCP performance, making it suitable for performance optimization studies. These parameters include wireless channel characteristics, ARQ/FEC settings, size of protocol data units at different layers, buffer size at the IP layer, and the raw data rate of the wireless channel.