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Status: Verified (2)

RFC 4585, "Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)", July 2006

Source of RFC: avt (rai)

Errata ID: 2853
Status: Verified
Type: Technical
Publication Format(s) : TEXT

Reported By: Ali Begen
Date Reported: 2011-07-05
Verifier Name: Robert Sparks
Date Verified: 2011-08-05

Section 4.2 says:

OLD:
      rtcp-fb-param      = SP "app" [SP byte-string]
                         / SP token [SP byte-string]
                         / ; empty
NEW:
      rtcp-fb-param      = [ SP "app" [SP byte-string]
                         / SP token [SP byte-string] ]


OLD:
      rtcp-fb-ack-param  = SP "rpsi"
                         / SP "app" [SP byte-string]
                         / SP token [SP byte-string]
                         / ; empty
NEW:
      rtcp-fb-ack-param  = [ SP "rpsi"
                         / SP "app" [SP byte-string]
                         / SP token [SP byte-string] ]


OLD:
      rtcp-fb-nack-param = SP "pli"
                         / SP "sli"
                         / SP "rpsi"
                         / SP "app" [SP byte-string]
                         / SP token [SP byte-string]
                         / ; empty
NEW:
      rtcp-fb-nack-param = [ SP "pli"
                         / SP "sli"
                         / SP "rpsi"
                         / SP "app" [SP byte-string]
                         / SP token [SP byte-string] ]

Notes:

During the AUTH48 of RFC 6285, we discovered a bug with the ABNF syntax in RFC 4585. The original ABNF in Section 4.2 (as noted above) is incorrect ("/ ;empty" is not a valid ABNF - RFC 5234 does not allow empty alternates).

The NEW text intends to fix it. There are 3 places where the same change should be applied (changes are identical).

Errata ID: 3313
Status: Verified
Type: Technical
Publication Format(s) : TEXT

Reported By: Mo Zanaty
Date Reported: 2012-08-11
Verifier Name: Robert Sparks
Date Verified: 2012-11-26

Section 4.2 says:

      rtcp-fb-ack-param  = SP "rpsi"
                         / SP "app" [SP byte-string]
                         / SP token [SP byte-string]
                         / ; empty

It should say:

      rtcp-fb-ack-param  = SP "rpsi"
                         / SP "app" [SP byte-string]
                         / SP token [SP byte-string]

Notes:

RFC 4585 defines and allows generic NACK (with no further parameters) but not generic ACK (which always requires further parameters). Section 4.2 says:
...
Parameters MUST be provided to further distinguish different types
of positive acknowledgement feedback.
...
The feedback type "nack", without parameters, indicates use of the
Generic NACK feedback format as defined in Section 6.2.1.
...
The ABNF incorrectly allows nothing after "ack", implying that generic ACK is valid. Even the approved errata, which replaces the invalid empty alternate with optional [], still allows nothing after "ack". Note that recent interest in RTP congestion control (e.g. RMCAT BOF) may lead to defining a standard ACK.

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