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Analytical Model of TCP with Enhanced Recovery Mechanism for Wireless Environments

In this paper, we extend the analytical model for the TCP steady state throughput as a function of the network utilization factor, round trip time and packet drop rate for unlimited data transfer to capture the fast retransmit and recovery mechanisms. These mechanisms are frequently activated on connections over wireless links. We model TCP with a modified fast retransmit algorithm that allows packet recovery with smaller congestion window sizes than possible with TCP Reno or NewReno, thereby reducing the likelihood of timeouts. We also propose a further modification that dynamically adjusts its congestion window by considering the packet drop rate as the input parameter. Simulations with the OPNET tool demonstrate that the model is able to predict TCP performance accurately over a wide range of packet loss rates. Moreover, simulation results show the performance of the modified TCP scheme is markedly superior to that of standard TCP Reno over a UMTS network.