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

[Christer Holmberg <[e-mail]>]

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.

Regards,

Christer