Performance analysis of token-based fast TCP in systems supporting large windows

Since TCP can only detect congestion after packet losses have already happened, various forms of fast TCP (FTCP) have been proposed to notify congestion early and avoid packet losses in intermediate nodes by effectively controlling backward ACK flows traversing the same nodes as the forward data packets. Among them, token-based FTCP (TB-FTCP) is a promising approach as it does not need to determine the rate of delaying ACK. The effectiveness of TB-FTCP has been proven for networks in which window size is limited by the bandwidth-delay product (see Peng, F. et al., Proc. 9th Int. Conf. on Computer Commun. and Networks, 2000). A mathematical model for the TB-FTCP is now presented and analyzed numerically for networks in which window size can be larger than the bandwidth-delay product. Results indicate that the proposed method performs extremely well compared to traditional TCP implementations. It is important to note that TCP behavior at end-nodes does not have to be modified in any way.