Congestion control is the process a network sender uses to determine the rate at which to send data. A congestion control algorithm balances sending sufficient data to make meaningful progress for a user with avoiding filling buffers in the network and overloading the network path. Better congestion control algorithms can help improve application performance, such as latency under load, while safeguarding overall network performance for all senders.

Specifying a congestion control algorithm can help implementers, operators, and other interested parties develop a shared understanding of how the algorithm works, how it is expected to behave in various scenarios and configurations, and can make it easier for them to suggest improvements and identify limitations.

Congestion control algorithm proponents now often have the opportunity to test and deploy at scale without IETF review. The set of protocols using these algorithms has spread beyond TCP and SCTP to include DCCP, QUIC, and beyond. There is more interest in specialized use cases such as data centers and real-time protocols. The community has gained much more experience with indications of congestion beyond packet loss.

The Congestion Control Working Group analyzes impediments to congestion control work occurring in the IETF and generalizes congestion control specifications to facilitate implementations for multiple relevant transport protocols. RFC 9473 specifies the Best Current Practice for evaluation of new congestion control proposals as Experimental or Proposed Standard RFCs. This encourages IETF review of congestion control proposals and standardization of mature congestion control algorithms.

The congestion control expertise in the working group makes it a natural venue to take on work related to indications of congestion such as delay, host queuing algorithms, rate pacing, multipath, interaction with other layers, among others. In particular, it can address congestion control algorithms with empirical evidence of safety (for example - avoiding congestion collapse) and stated intent to deploy by major implementations. The working group is intended to be a home for such work, and it is chartered to adopt proposals in this space.

The group will coordinate closely with other relevant working and research groups, including ICCRG, TCPM, QUIC, and TSVWG. Documents in CCWG will remain as transport protocol agnostic as possible, but they may have short specific instructions, such as header options or parameter formats, for one or more protocols. Documents that are wholly specific to mechanisms in a single protocol will remain in the maintenance working group for that protocol. Algorithms proposed for Experimental status, in consultation with ICCRG, based on an assessment of their maturity and likelihood of near-term wide-scale deployment, are in scope.

Publication of Informational RFCs analyzing the published standard congestion control algorithms is within CCWG scope. However, it is not chartered to document the state of congestion control in the Internet, including assessments of whether any particular implementation complies with existing standards. Other venues, such as the IRTF, may be more appropriate for publishing such documents.