Subject: WG Action: Formed RTP Media Congestion Avoidance Techniques (rmcat)

From: The IESG <[email-masked]>
Date: Fri, 21 Sep 2012 09:53:53 -0700

A new IETF working group has been formed in the Transport Area. For
additional information please contact the Area Directors or the WG
Chairs.

RTP Media Congestion Avoidance Techniques (rmcat)
------------------------------------------------
Current Status: Proposed Working Group

Chairs:
  Lars Eggert <[email-masked]>
  Mirja Kuehlewind <[email-masked]>

Assigned Area Director:
  Wesley Eddy <[email-masked]>

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Charter 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 algorithm; in this case it 
      will be one of the objects of the experimentation to determine the 
      applicabilities and relative merits of the algorithms.
    - 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 there are significant flaws,
      such as ones that turn out to be harmful to flows using or
      competing with them. If so, the WG will write a document
      describing the issues encountered and recommending to the IESG
      to move the specification to Historic status. 

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
    - Requirements for RTCP extensions for use with congestion control 
      algorithms as an input to the AVTCORE WG.
    - 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

Milestones:
  Dec 2012 - Adopt first WG drafts of requirements and evaluation
criteria
  Dec 2012 - Adopt first WG draft of RTCP extensions for use with
congestion control algorithms and interactions between applications and
RTP flows (if needed)
  Jan 2013 - Adopt first congestion control candidate as WG draft
  Jan 2013 - Adopt first WG draft on identifying and controlling groups
of flows
  Mar 2013 - Submit requirements and evaluation criteria to IESG as
Informational
  May 2013 - Submit RTCP extension requirements for use with congestion
control algorithms to AVTCORE (if needed)
  May 2013 - Submit interactions between applications and RTP flows to
IESG as Informational
  Jun 2013 - Submit first congestion control candidate to IESG for
Experimental publication
  Jul 2013 - Submit identifying and controlling groups of flows to IESG
for Standards Track publication
  Sep 2013 - Publish first draft of evaluation results
  Sep 2013 - Publish first draft of Standards Track congestion control
algorithm
  Sep 2013 - Publish first draft of techniques to detect, instrument or
diagnose failing to meet RT schedules
  Mar 2014 - Submit techniques to detect, instrument or diagnose failing
to meet RT schedules to IESG as Informational
  May 2014 - Submit congestion control to IESG for Proposed Standard