To make this more explicit, I added the following paragraphs at theSince silence suppression is just the absence of packets, its not clear what it means to "accept" it.
beginning of Section 4.1 in the A/V profile:
Since the ability to suppress silence is one of the primary
motivations for using packets to transmit voice, the RTP header
carries both a sequence number and a timestamp to allow a receiver to
distinguish between lost packets and periods of time when no data was
transmitted. Discontiguous transmission (silence suppression) MAY be
used with any audio payload format. Receivers MUST accept silence
suppression unless its use is restricted by signaling specified
elsewhere.
This sentence and the previous appear contradictory to me. The previous says that you won't need to handle silence suppression if signaling says its not in use, but this sentence says you need it anyway.(Even if the transmitter does not suppress silence, the receiver must be prepared to handle periods when no data is present since packets may be lost.)
Some payload formats define a "silence insertion descriptor" or "comfort noise" frame to specify parameters for artificial noise that may be generated during a period of silence to approximate the background noise at the source. For other payload formats, a generic Comfort Noise (CN) payload format is specified in RFC 3389 [9]. When the CN payload format is used with another payload format, different values in the RTP payload type field distinguish comfort-noise packets from those of the selected payload format.
I assume [9] is an informative reference, not normative.
Presumably RFC YYYY [7] will be at proposed. The above text seems to me to provide a normative reference to that specification. A draft standard cannot have a normative reference to a proposed standard.In addition, I added the following first sentence in the four places where the sentences similar to the second one appear in G723 and G729*: Receivers MUST accept comfort noise frames if restriction of their use has not been signaled. The MIME registration for G729 in RFC YYYY [7] specifies a parameter that MAY be used with MIME or SDP to restrict the use of comfort noise frames.