[R-C] Feedback mechanisms

[Mo Zanaty (mzanaty)]

Michael Welzl <michawe at ifi.uio.no> wrote:
> ...piggybacking ACKs on RTP payload...

Randell Jesup <randell-ietf at jesup.org> wrote:
> ...use header extensions as an alternate channel for RTCP...

Several implementations do either or both of these things, in proprietary ways obviously. I think both should be standardized, although this may be an unpopular view in AVT.

Note that there is no standardized generic ACK. I just submitted an errata to the RFC 4585 ABNF to clarify that "ack" (without parameters) is invalid since there is no generic ACK. There is only "ack rpsi" which is specific to H.263 Annex N, and "ack app" which is proprietary.

Beyond ACK, many other types of RTCP feedback would benefit from the efficiency of piggybacking in RTP header extensions. (NACK, ECN, FIR, TMMBR, PLI, SLI, etc.) So a general mechanism for all RTCP feedback may be more useful than a single mechanism for ACKs.

Mo