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

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

Please see inline comments marked under <Raju4>


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.



<Christer3> The idea was to not use a=setup for any "type" of SCTP, including native SCTP.

<Raju4>

I see. The SCTP draft-ietf-mmusic-sctp-sdp is obviously not yet updated as it still has a=setup based semantics.

</Raju4>



BR

Raju



Regards,



Christer