Description of Working Group Today's Internet traffic includes interactive real-time media, which is often carried via sets of 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. Congestion control algorithms for interactive real time media may need to be quite different from the congestion control of TCP: for example, some applications can be more tolerant to loss than delay and jitter. The set of requirements for such an algorithm includes, but is not limited to: - Low delay and low jitter for the case where there is no competing traffic using other algorithms - Reasonable share of bandwidth when competing with RMCAT traffic, other real-time media protocols, and ideally also TCP and other protocols. A 'reasonable share' means that no flow has a significantly negative impact [RFC5033] on other flows and at minimum that no flow starves. - 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. This must be completed prior to finishing any Experimental algorithm specifications. - Identify interactions between applications and RTP flows to enable conveying helpful cross-layer information such as per-packet priorities, flow elasticity, etc. This information might be used to populate an API, but the WG will not define a specific API itself. - Determine if extensions to RTP/RTCP are needed for carrying congestion control feedback, using DCCP as a model. If so, provide the requirements for such extensions to the AVTCORE working group for standardization there. - Develop techniques to detect, instrument or diagnose failing to meet RT schedules due to failures of components outside of the charter scope, possibly in collaboration with IPPM. - Develop a mechanism for identifying shared bottlenecks between groups of flows, and means to flexibly allocate their rates within the aggregate hitting the shared bottleneck. - Define evaluation criteria for proposed congestion control mechanisms, and publish these as an Informational RFC. This must be completed prior to finishing any Proposed Standard algorithm specifications. - 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 evaluation criteria and the result of experimentation with these Experimental algorithms on the Internet. This must be completed prior to finishing any Proposed Standard algorithm specifications. - 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. - For each of the Experimental algorithms that have not been selected for the Standards Track, the working group will review the algorithm and determine whether the RFC should be moved to Historic status via a document that briefly describes the issues encountered. This step is particularly important for algorithms with significant flaws, such as ones that turn out to be harmful to flows using or competing with them. The work will be guided by the advice laid out in RFC 5405 (UDP Usage Guidelines), RFC 2914 (congestion control principles), and RFC5033 (Specifying New Congestion Control Algorithms). The following topics are out of scope of this working group, on the assumption that work on them will proceed elsewhere: - 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 - Defining active queue management algorithms or modifications to TCP of any kind - Multicast congestion control; common control of multiple unicast flows is in scope - Topologies other than point-to-point connections; implications on multi-hop connections will be considered at a later stage 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 coordinate closely with other Transport area groups working on congestion control, and with the Internet Congestion Control Research Group of the IRTF. Deliverables: - Requirements for congestion control algorithms for interactive real time media as an Informational RFC - Evaluation criteria for congestion control algorithms for interactive real time media as an Informational RFC - RTCP extensions for use with congestion control algorithms as a Proposed Standard RFC - Interactions between applications and RTP flows as an Informational RFC - Identifying and controlling groups of flows as a Proposed Standard RFC - Techniques to detect, instrument or diagnose failing to meet RT schedules as either an Informational RFC or on the Standards Track if needed for interoperability or other aspects that would justify it. - Candidate congestion control algorithm for interactive real time media as Experimental RFCs (likely more than one) - Experimentation and evaluation results for candidate congestion control algorithms as an Informational RFC - One or more recommended congestion control algorithms for interactive real time media as Proposed Standard RFCs