[AVT] Profile: G.729 vs G.729A

[Stephen Casner <casner@acm.org>]

In October, I received a message from Don Stanwyck who was seriously
concerned because the RTP A/V profile and draft-ietf-avt-rtp-mime-06
did not specify any way to signal G.729A as distinct from G.729.  My
interpretation of his concern was that because we only have a MIME
type "G729" that an endpoint which only implemented the less-complex
G.729A algorithm would not be compliant.  He assumed that negotiating
G729 payload format implied a resource commitment for the more complex
algorithm.

The reason we define only one payload format and one MIME type for RTP
is that the G.729 and G.729A algorithms are interoperable.  To make
this clear, I have added the following text:

OLD
   A reduced-complexity version of the G.729
   algorithm is specified in Annex A to Rec. G.729.  The speech coding
   algorithms in the main body of G.729 and in G.729 Annex A are fully
   interoperable with each other, so there is no need to further
   distinguish between them.
NEW ADDITION:
   An implementation that signals or accepts
   use of G729 payload format may implement either G.729 or G.729A
   unless restricted by additional signaling specified elsewhere related
   specifically to the encoding rather than the payload format.

                                                        -- Steve

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