Re: [MMUSIC] draft-ietf-mmusic-sctp-sdp-07 SCTP SDP syntax question

Paul Kyzivat <pkyzivat@alum.mit.edu> Thu, 02 October 2014 01:37 UTC

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From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: Re: [MMUSIC] draft-ietf-mmusic-sctp-sdp-07 SCTP SDP syntax question
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On 10/1/14 7:57 PM, Christian Groves wrote:
> What is the status of the draft-ejzak-mmusic-data-channel-sdpneg-00?

I don't know the status. The thought Keith Drage had indicated that he 
was picking up responsibility for it.

	Thanks,
	Paul

> It has expired and is based on the old SDP SCTP syntax. Particularly the
> example in cl.4:
>
>     m=application 54111 DTLS/SCTP 5000 5001 5002
>     c=IN IP4 79.97.215.79
>     a=sctpmap:5000 webrtc-datachannel
>     a=sctpmap:5001 bfcp
>     a=sctpmap:5002 t38
>
> Wouldn't apply if we're saying to use multiple m-lines.
>
> I guess cl.5.1.1.3 would use the same Websocket subprotocol name
> registry as data channel does?
>
> Regards, Christian
>
> On 2/10/2014 12:14 AM, Paul Kyzivat wrote:
>> On 10/1/14 3:44 AM, Christian Groves wrote:
>>
>>>> <Sal>
>>>> there have been several discussion about the ability to have more than
>>>> one usage of the SCTP association,
>>>> and has been agreed not to allow it.
>>>> So each 'm' line describes a single SCTP association;  each
>>>> association has only one single specify usage.
>>>> </Sal>
>>>
>>> [CNG] So how would I specify in SDP a scenario where BFCP uses a
>>> DTLS/SCTP association and MSRP uses a DTLS/SCTP association where they
>>> both use the same DTLS connection? Are these to be separate m-lines?
>>
>> To have two different SCTP associations over the same DTLS connection,
>> they would have to be distinguished by sctp-port. To achieve that you
>> could write two m-lines. They would share the same ip address and
>> port, and would have different "a=sctp-port" lines. Then they would
>> have to be bundled.
>>
>> Doing that would require extending the definition of bundle to cover
>> that case. (There is no *technical* problem in doing this.)
>>
>> OTOH, in principle they don't need their own SCTP association. AFAIK
>> they each only use one sctp stream-pair (channel). If they could agree
>> on how to choose channels then they could share an SCTP association.
>> That is where draft-ejzak... comes in.
>>
>>     Thanks,
>>     Paul
>>
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