WG charter - input to Vancouver

This is a charter based on the one suggested in December 2011, but substantially rewritten. It is an input document.
See also the naming subpage.

RTP Media Congestion Avoidance Techniques (rmcat)

Status: Proposed Working Group
Last Updated: 2012-05-18


Transport Area Director(s):
 Wesley Eddy <wes@mti-systems.com>

Transport Area Advisor:
 Wesley Eddy <wes@mti-systems.com>

Mailing Lists: TBD (until establishment, we use rtp-congestion@alvestrand.no)

Description of Working Group

In today's current internet, part of the traffic is delivery of interactive real time media, often in the form of sets of media flows using RTP over UDP.
There is no generally accepted congestion control mechanism for this kind of data flow.
With the deployment of applications using the RTCWEB protocol suite, the number of such flows is likely to increase, especially non-fixed-rate flows such as video or adaptive audio. There is therefore some urgency in specifying one or more congestion control mechanisms that can find general acceptance.

The set of requirements for such an algorithm includes, but is not limited to:
  • Low delay for the case where there is no competing traffic using other algorithms
  • Fair share of bandwidth when there is competing traffic using other algorithms
  • Effective use of signals like packet loss and ECN markings to adapt to congestion
The working group will:
  • Develop a clear understanding of the congestion control requirements for RTP flows, and document deficiencies of existing mechanisms such as TFRC with regards to these requirements
  • Determine if there is an appropriate means to define standard RTP/RTCP extensions for carrying congestion control feedback, similar to how DCCP defines CCIDs, and if so, document such extensions as standards-track RFCs.
  • Define evaluation criteria for proposed mechanisms, and publish these as an Informational RFCs.
  • Find or develop candidate congestion control algorithms, verify that these can be tested on the Internet without significant risk, and publish one or more of these as Experimental RFCs.
  • Publish the result of experimentation with these Experimental algorithms on the Internet
  • Once an algorithm has been found or developed that meets the evaluation criteria, and has a satisfactory amount of documented experience on the Internet, publish this algorithm as a Standards Track RFC. There may be more than one such algorithm.
The work will be guided by the advice laid out in RFC 5405 (UDP usage guidelines) and RFC 2914 (congestion control principles).

The following topics are out of scope:
  • Circuit-breaker algorithms for stopping media flows when network conditions render them useless; this work is done in AVTCORE;
  • Media flows for non-interactive purposes like stored video playback; those are not as delay sensitive as interactive traffic;
  • Active queue management; modifications to TCP of any kind; and
  • Multicast congestion control (common control of multiple unicast flows is in scope).
The working group is expected to work closely with the RAI area, including the underlying technologies being worked on in the AVTCORE and AVTEXT WGs, and the applications/protocol suites being developed in the  CLUE and RTCWEB working groups.
It will also liaise closely with other Transport area groups working on congestion control, and with the Internet Congestion Control Research Group of the IRTF.


  • Evaluation criteria for congestion control algorithms for interactive real time media - Informational RFC
  • RTCP extensions for use with congestion control algorithms - Standards-track RFC
  • Candidate congestion control algorithm for interactive real time media - Experimental RFCs (likely more than one)
  • Experimentation and evaluation results for candidate congestion control algorithms - Informational RFC
  • A recommended congestion control algorithm for interactive real time media - Standards-track RFC 


  • NN NNNA: (chartering + 1 month) Publish first draft of evaluation crieria
  • NN NNNB: Adopt first congestion control candidate as WG draft
  • NN NNNC: (A + 4 months) Submit evaluation criteria to IESG as Informational
  • NN NNND: (C + 1 month) Submit first congestion control candidate to IESG for Experimental publicaiton
  • NN NNNE: (D + 3 months) First draft of evaluation results
  • NN NNNF: (=E) First draft of standars-track congestion control
  • NN NNNG: (F + 6 months) Submit congestion control to IESG for Proposed Standard
(time from chartering to end of charter is 15 months)