Subject: [AVT] RTP No-Op and AVP Feedback

From: "Dan Wing" <[email-masked]>
Date: Fri, 14 Oct 2005 17:11:54 -0700

Draft-ietf-avt-rtp-no-op provides several functions:

  1. A non-operation packet with clear semantics that can be
     negotiated as part of offer / answer;

  2. A mechanism to request a receiver to send RTCP earlier than the
     receiver would normally send RTCP.

The functions of (1) are useful as a keepalive packet when an RFC3389
silence packet is inappropriate.  Examples include T.38 over RTP, text
over RTP (RFC4103), or video codecs.

The functions of (2) are useful for probing network behavior before,
during, or after an RTP session.

Currently RTP No-Op is restricted to the RTCP-based feedback profile
of RTP (RTP/AVPF).  This significantly reduces is utility of both
(1) and (2).

As RFC3550 already allows unicast senders to send RTCP immediately:

 >
 >  o  For unicast sessions, the reduced value MAY be used by
 >     participants that are not active data senders as well, 
 >     and the delay before sending the initial compound RTCP 
 >     packet MAY be zero.
 >

the authors consider it appropriate for RTP No-Op's "Request Early
RTCP" bit to allow unicast sessions which support RTP No-Op in offer /
answer to send RTCP reports immediately upon receipt of a No-Op packet
with the "Request Early RTCP" bit set.  We need to adhere to section
6.2 of RFC3550 and the rules of whatever profile we're using, but we'd
like to remove the requirement that No-Op can only use AVPF.

Any comments on this direction?

-d

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