The Effect of the Initial Window Size and Limited Transmit Algorithm on the Transient Behavior of TCP Transfers

We study the impact of the modifications proposed for TCP in the context of short file transfers. The two most important proposals are the increment of the initial window size (IW) [3] and the Limited Transmit algorithm (LT) [1]. We analyze analytically and by simulations the effect of these proposals on the TCP latency. We demonstrate that the LT proposal reduces the TCP latency similarly to the IW proposal however LT is less aggressive than IW. Nevertheless, in the context of short file transfers we point out a scenario, when upon a single packet loss the sender times out even if IW or LT are enabled. This harmful scenario happens when the very last packets of the file transfer are lost. Therefore to avoid this situation we propose a new modification which is based on reducing the number of duplicate acknowledgements TCP reacts to. In order to avoid the potentially harmful effect of needless retransmissions on the network load we suggest to implement the new modification only for short file transfers.

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