Re: [MMUSIC] Single SCTP usage per SDP session?

[Paul Kyzivat <[e-mail]>]

On 12/2/14 11:48 AM, Christer Holmberg wrote:
> Hi,
>
>>>>>> Per my understanding, draft-ietf-tsvwg-sctp-dtls-encaps just talks about SCTP over DTLS and allowing multiple SCTP associations, which is perfectly fine.
>>>>>> Then it is possible to come up with SCTP-SDP semantics to use that capability.
>>>>>> One m= line allowing one SCTP over DTLS limit is fine. Using BUNDLE
>>>>>> you can replicate same 4-tuple in multiple m= lines. Then there is only one DTLS association established and multiple SCTP associations over that is possible (one per >>>>> m= line).
>>>>>> If BUNDLE is not used then I believe same 4-tuple on multiple m=
>>>>>> lines are NOT possible. This is because, per my understanding, unlike TCP/native-SCTP used under non- ICE
>>>>>> environments, in ICE-environments the TCP/UDP port specified is used both as client and server port for DTLS.
>>>>>
>>>>> Even with BUNDLE, you would have to use the same m= line port value from the beginning, which is not allowed. So, you basically would have to add the additional >>>> SCTPoDTLS m= lines once the usage of BUNDLE has been negotiated.
>>>>
>>>> bundle-only would allow you to set this up.
>>>
>>> Correct.
>>>
>>> But, then we would need to have rules saying that you are not allowed to move an m= line associated with a SCTP usage out of the BUNDLE group, etc.
>>
>> How is this different from any other bundle-only m-line?
>
> bundle-only is used to ensure that an m- line is only accepted by the answerer if accepted into a BUNDLE group. Currently nothing prevents the offerer to, in a later offer, move that m- line out of that BUNDLE group.

And that is no different here. If you bundled multiple SCTP 
associations, each on a separate SCTP port, then you can take them out 
of the bundle, each on its own addr/udp-port.

If you want to take more than one out, you can put each on its own udp 
port, or you could group them together in a second (new) bundle, again 
using bundle-only for all but the first in that bundle.

This is very similar to the situation with RTP, except that you must use 
bundle-only when there is more than one in a bundle.

	Thanks,
	Paul