[rtcweb] Review of draft-ietf-rtcweb-rtp-usage

[Bernard Aboba <[e-mail]>]

Here are a few things that caught my eye in re-reading
draft-ietf-rtcweb-rtp-usage:

Circuit Breaker requirements

Section 7.1

   In the absence of a concrete congestion control algorithm, all WebRTC
   implementations MUST implement the RTP circuit breaker algorithm that
   is described in
[I-D.ietf-avtcore-rtp-circuit-breakers<http://tools.ietf.org/html/draft-ietf-rtcweb-rtp-usage-13#ref-I-D.ietf-avtcore-rtp-circuit-breakers>].


[BA] What does "concrete" mean here?  There are a number of congestion
control algorithms that one might or might not consider "concrete".  Also
at various meetings, I have heard people talk about implementation of
Circuit Breakers along with congestion control algorithms.

Personally, I would consider sender-side congestion control algorithms to
qualify as "concrete", assuming that the algorithm could function
adequately when interacting with standards-based implementations only
supporting the functionality described in the RTP usage document (e.g. RTCP
reports, etc.).  I am not sure that receiver-side congestion control
mechanisms should qualify as "concrete" if they require both sender and
receiver to implement proprietary functionality for congestion control to
function adequately.

SDP dependencies

Since WebRTC is signaling-independent, at various points in discussion of
the RTP usage document, it has been pointed out that it is not appropriate
to mandate SDP signaling.  However, in re-reading the draft, a number of
SDP mandates still remain.  I'd like to see these changed to state the
requirement more generically, with guidance provided on what to do if SDP
signaling is used.

Section 4.8

   Implementations are REQUIRED to support signalled RTP synchronisation
   source (SSRC) identifiers, using the "a=ssrc:" SDP attribute defined
   in Section 4.1<http://tools.ietf.org/html/draft-ietf-rtcweb-rtp-usage-13#section-4.1>and
Section 5
of [RFC5576] <http://tools.ietf.org/html/rfc5576#section-5>.
Implementations MUST also
   support the "previous-ssrc" source attribute defined in Section 6.2 of
[RFC5576] <http://tools.ietf.org/html/rfc5576#section-6.2>.  Other per-SSRC
attributes defined in [RFC5576 <http://tools.ietf.org/html/rfc5576>] MAY be
   supported.

Propose this be changed to:


   Implementations are REQUIRED to support signalled RTP synchronisation
   source (SSRC) identifiers.  In an SDP context, this can be done using
the "a=ssrc:" SDP attribute defined in Section
4.1<http://tools.ietf.org/html/draft-ietf-rtcweb-rtp-usage-13#section-4.1>and
Section 5
of [RFC5576] <http://tools.ietf.org/html/rfc5576#section-5> in addition
to the "previous-ssrc" source attribute defined in Section 6.2; other
per-SSRC attributes defined in [RFC5576 <http://tools.ietf.org/html/rfc5576>]
MAY be supported.