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

["Makaraju, Maridi Raju (Raju)" <[e-mail]>]

Please see comments under <Raju3> tags.


<Christer> This was discussed in Honolulu, and the agreement was that the setup attribute will NOT be used to determine who initiates the SCTP association. Instead BOTH endpoints are supposed to trigger the initiation. The setup attribute will only be used to determine the TLS role.

<Raju2>

2 use cases:

1.SCTP over DTLS: For this yes, a=setup is for DTLS.

  The sctp port usage needs be clarified indicating it is the server port, not the client port.



<Christer2> Yes.





2.Native SCTP: I believe a=setup is for SCTP association.

When a=setup:passive/actpass is used the sctp port usage needs to be clarified indicating it is the server port. When a=setup:active is used port must be 9 (discard port). This needs clarification as well.

Both sides trying to open SCTP simultaneously is probably ok because SCTP allows them to be converted into single association if there are simultaneous INITs (or INIT chunk received in ESTABLISHED state) on the same 4-tuple. This is per RFC 4960 section 5.2.1<http://tools.ietf.org/html/rfc4960#section-5.2.1> and 5.2.2<http://tools.ietf.org/html/rfc4960#section-5.2.2> .

But the key here is same 4-tuple, which means the client must use same **server port** to initiate an outgoing association. If this is not done then, the end result will be 2 SCTP associations setup and/or one of them may be rejected and may depend on implementation.

So, I believe some clarifications are needed in this area.



<Christer2> So, assuming we don't use (per the agreement in Honolulu) a=setup for the SCTP association, we would need to mandate (or, at least say SHOULD) usage of the server port also to initiate an outgoing association, in order to avoid 2 SCTP associations.



But, that also applies to SCTP over DTLS, doesn't it?

<Raju3>

Sorry, it actually ONLY applies to SCTP over DTLS. I misplaced the above description under "native SCTP" instead of "SCTP over DTLS". For native SCTP, as discussed, a=setup negotiation determines which side initiates SCTP association, so the semantics are very clear here.

</Raju3>



BR

Raju