Proportional Rate Reduction
RFC 9937, “Proportional Rate Reduction”, is a Proposed Standard document published in December 2025 by M. Mathis, N. Cardwell, Y. Cheng, N. Dukkipati. It obsoletes RFC 6937. The canonical text is published by the RFC Editor.
Abstract
This document specifies a Standards Track version of the Proportional Rate Reduction (PRR) algorithm that obsoletes the Experimental version described in RFC 6937. PRR regulates the amount of data sent by TCP or other transport protocols during fast recovery. PRR accurately regulates the actual flight size through recovery such that at the end of recovery it will be as close as possible to the slow start threshold (ssthresh), as determined by the congestion control algorithm.
What “Proposed Standard” means
An entry-level standards-track specification: stable, peer-reviewed and a solid basis for implementation, though it may still evolve before becoming an Internet Standard.
The canonical text of RFC 9937 is hosted at rfc-editor.org. Available in HTML,TXT,PDF,XML.
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