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Re: [AVT] 2833bis





    "Since all implementations MUST be able to receive events 0 through

   15, listing these events in the a=fmtp line is OPTIONAL.



There was some discussion about how appropriate this really was, and I 
believe

it was generally agreed, that mandating that all implementations of 
RFC 2833

support DTMF was not the right thing to do. For example, if I only want to

convey V.25/V.8 ANS and ANSam, then why not ? Thus, the following 
implementation

note was added at http://www.cs.columbia.edu/~hgs/rtp/payload_audio.html:



    "Implementations can support events 0 through 15 (DTMF) by simply 
ignoring

the packets, but MUST declare all event numbers that are meaningful to 
it in the

fmtp parameter, including 0 through 15."



Taking a look at Section 3.9 in 2833bis, I see the offending text is 
no longer

there. If it doesn't say anything else about mandatory and implied 
DTMF support

anywhere else, then I'm happy.



If somebody finds a reference to something suggesting that this be 
mandatory, let me know. I don't know if this is a problem, but since 
listing 0-15 was OPTIONAL in 2833, we could stipulate that fmtp is 
mandatory now. In the spirit of limiting options and being explicit 
about capabilities, I see no drawback to making it mandatory.




I like the soft-state idea. It has some nice self-synchronizing 
properties that

would seem to make the whole "state" concept less susceptible to 
errors (whether

human or network induced). 


I will add this unless somebody objects. This was implied, since there 
was no text that ruled out non-zero durations for events marked as 
'state?', but it can't hurt to call this out explicitly.




If there are "good til cancelled" states that need to

be communicated to the other party, and for which the soft-state 
approach is not

acceptable or desirable, then I wonder if a call control protocol 
wouldn't be a

more appropriate means of signaling such things.



-- Flemming






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