Subject: [secdir] [new-work] WG Review: RTP Media Congestion Avoidance Techniques (rmcat)

From: IESG Secretary <[email-masked]>
Date: Wed, 05 Sep 2012 15:20:12 -0700

A new IETF working group has been proposed in the Transport Area. The
IESG has not made any determination yet. The following draft charter was
submitted, and is provided for informational purposes only. Please send
your comments to the IESG mailing list (iesg at ietf.org) by 2012-09-12.

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

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

Charter of Working Group:

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

Milestones:
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