Re: [AVT] Profile: Silence suppression is allowed by default

[Colin Perkins <csp@csperkins.org>]

--> Jonathan Rosenberg writes:
>I think this addition is great. I have seen this issue come up all the 
>time. Some comments on the wording inline:
>
>Stephen Casner wrote:
>
>> To make this more explicit, I added the following paragraphs at the
>> 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.  
>
>Since silence suppression is just the absence of packets, its not clear 
>what it means to "accept" it.
>
>> (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.)
>
>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.
>
>I would propose the last two sentences be replaced with:
>
>Receivers MUST be prepared to handle the absence of packets for an 
>arbitrary period of time in order to accomodate silence suppression at 
>the sender. This applies even if silence suppression is not in use 
>(which can be known to the receiver through signaling, outside the scope 
>of this specification), because packet loss cannot be distinguished from 
>silence suppression.

This is not accurate either, since you can distinguish loss from silence
suppression using the sequence number. We could change the last few words
to "because packet loss may cause arbitrary gaps in reception", or similar?

Colin
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