This article discusses several changes to TCP's congestion control, either proposed or in progress. The changes to TCP include a limited transmit mechanism for transmitting new packets upon receipt of one or two duplicate acknowledgments, and a SACK-based mechanism for detecting and responding to unnecessary fast retransmits or retransmit timeouts. These changes to TCP are designed to avoid unnecessary retransmit timeouts, to correct unnecessary fast retransmits or retransmit timeouts resulting

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... from reordered or delayed packets, and to assist the development of viable mechanisms for corruption notification. The changes in the network include explicit congestion notification, which builds on the addition of active queue management.