Proportional Rate Reduction for TCP

Document Type Replaced Internet-Draft (individual)
Last updated 2012-04-19 (latest revision 2011-07-11)
Replaced by RFC 6937
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


This document describes an experimental algorithm, Proportional Rate Reduction (PPR) and related algorithms to improve the accuracy of the amount of data sent by TCP during loss recovery. Standard Congestion Control requires that TCP and other protocols reduce their congestion window in response to losses. This window reduction naturally occurs in the same round trip as the data retransmissions to repair the losses, and is implemented by choosing not to transmit any data in response to some ACKs arriving from the receiver. Two widely deployed algorithms are used to implement this window reduction: Fast Recovery and Rate Halving. Both algorithms are needlessly fragile under a number of conditions, particularly when there is a burst of losses that such that the number of ACKs returning to the sender is so small that the effective window falls below the target congestion window chosen by the congestion control algorithm. Proportional Rate Reduction avoids these excess window reductions such that at the end of recovery the actual window size will be as close as possible to the window size determined by the congestion control algorithm. It is patterned after rate halving, but using the fraction that is appropriate for target window chosen by the congestion control algorithm. In addition we propose two slightly different algorithms to bound the total window reduction due to all mechanisms, including application stalls, the losses themselves and inhibit further window reductions when possible.


Matt Mathis (
Nandita Dukkipati (
Yuchung Cheng (

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)