Monday, May 11, 2009
Why does Snoop suppress the duplicate TCP acknowledgements it receives after retransmitting lost packets?
Snoop suppresses the duplicate TCP acknowledgements to avoid triggering end-to-end TCP retransmissions and congestion control. A Snoop agent maintains state for each TCP connection traversing the wireless gateway. TCP data packets sent from the wired to the wireless host are cached locally, until TCP acknowledgments from the wireless host verify that they were received. When duplicate acknowledgments arrive, indicating that a packet was lost, the packet is retransmitted by the agent from its local cache. The duplicate acknowledgments are then suppressed. This avoids conflicting local and TCP retransmissions by suppressing duplicate TCP acknowledgments while local error recovery.