Optimization of TCP segment size for file transfer
by R. M. Bournas
In this paper, we study the problem of optimal Transmission Control Protocol (TCP) segment size for file transfer from hosts to clients. The criterion of optimality is the minimization of the amount of TCP and IP (Internet Protocol) processing by the sender. The parameters that govern the host-processing cost include the cost for processing both the outgoing TCP segments and incoming TCP acknowledgments, the TCP window size, the maximum transferable unit (MTU) size of the network, and the network reliability factor. We study the variations of the sender processing cost as a function of the TCP segment size and the network reliability factor. We show that there exists a network reliability factor γ0 such that 1) for all network reliability factors γ ≤ γ0, the optimal TCP segment size equals the MTU size less the sizes of the TCP and IP headers (the sender processing cost increases with the TCP segment size in this case); and 2) for each γ > γ0 , there exists an optimal TCP segment size that is greater than the MTU size. Moreover, the optimal TCP segment size is an increasing function of the network reliability factor. We also derive a sufficient condition for the optimal TCP segment size to be greater than the MTU size. In this case, a lower bound for the optimal TCP segment size can be obtained as a simple function of the network reliability factor.