This document specifies an update to the round-trip time (RTT) estimation algorithm used for TFRC (TCP-Friendly Rate Control) congestion control by the Datagram Congestion Control Protocol (DCCP). It updates specifications for the CCID-3 and CCID-4 Congestion Control IDs of DCCP.

The update addresses parameter-estimation problems occurring with TFRC-based DCCP congestion control. It uses a recommendation made in the original TFRC specification to avoid the inherent problems of receiver-based RTT sampling, by utilising higher-accuracy RTT samples already available at the sender.

It is integrated into the feature set of DCCP as an end-to-end negotiable extension.