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

Hi there,

in order to provide a clear and readable answer I am answering directly the first mail of the thread.
See in line

br
Salvatore

On Nov 25, 2014, at 10:33 AM, Christer Holmberg <christer.holmberg@ericsson.com<mailto:christer.holmberg@ericsson.com>> wrote:

Hi,

Hopefully there are some SCTP experts in da hause that can clarify the following:

Previously, in the SCTP-SDP discussions, we have agreed that for a given SCTP/SCTPoDTLS/DTLSoSCTP association, we will only allow a single usage (e.g. a webrtc-datachannel).

So, if one wants multiple usages, one needs to establish multiple associations, using multiple m- lines.

BUT, according to RFC 4960, two SCTP endpoints MUST NOT have more than one SCTP association between them at any given time. Not exactly sure why, but that is what the text says…

“SCTP association: A protocol relationship between SCTP endpoints,
                composed of the two SCTP endpoints and protocol state information
                including Verification Tags and the currently active set of
                Transmission Sequence Numbers (TSNs), etc.  An association can be
                uniquely identified by the transport addresses used by the
                endpoints in the association.  Two SCTP endpoints MUST NOT have
                more than one SCTP association between them at any given time.”

<Sal>
That is not a problem.
As it has also already suggested it is enough to use a different port number on one side.
</Sal>

Now, does that mean that, for a given SDP session, we can only have a single SCTP m- line (read: single SCTP usage)?

For WebRTC usage that is probably enough, as we use SCTP only for the data channel, but in general…

<Sal>
note also that in https://tools.ietf.org/html/draft-ietf-tsvwg-sctp-dtls-encaps-06
we already have the following text that implies that is possible to have multiple SCTP
associations between two endpoints

   o  Multiple SCTP associations MAY be multiplexed over a single DTLS
      connection.  The SCTP port numbers are used for multiplexing and
      demultiplexing the SCTP associations carried over a single DTLS
      connection.

I hope it helps to clarify the issue.
</Sal>

Regards,

Christer
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