Re: [MMUSIC] JSEP Issue #394: What appears in m= lines.

Roman Shpount <roman@telurix.com> Tue, 10 January 2017 18:08 UTC

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From: Roman Shpount <roman@telurix.com>
Date: Tue, 10 Jan 2017 13:08:07 -0500
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Subject: Re: [MMUSIC] JSEP Issue #394: What appears in m= lines.
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We can do the registration for ICE transport tag in ICE-SIP-SDP. ICE tag
will indicate that ICE is required for this offer/answer exchange to
succeed. When ICE transport tag is used, c= and m= SDP line would carry no
address information and will contain "c=IN IP4 0.0.0.0" and port 9 in the
m= line. Also, if ICE/ transport tag is used, we should remove the
requirement for a re-INVITE after ICE nomination process is complete, since
it serves no purpose when no address is specified in c= and m= lines.

If we are not going to define ICE/ transport, then I propose the following:

1. When c= line is set to "IN IP4 0.0.0.0" and m= line is set to port 9, so
that these lines carry no valid address information as it is specified in
JSEP, protocol should be UDP/DTLS/SAVPF for RTP or UDP/DTLS/SCTP for data

2. When c= line and m= line carry valid address information, protocol
should match the candidate specified in c= and m= lines.

3. In cases when c= line and m= line carry valid address information, when
initial offer and answer are generated, they must include UDP candidates
and UDP candidates must be used as defaults. Once ICE nomination process is
complete, only the active candidate pair MUST be included in SDP, and the
transport for the active pair must be used.

I am not sure about the proper procedure for c= and m= lines during the ICE
nomination process, since active candidate can change during the
offer/answer exchange which can cause protocol line mismatch. One option is
to continue re-sending the initial offer and answer.

P.S. In the quoted text someone mentioned "UDP/TLS/RTP/SAVPF", should it be
"UDP/DTLS/RTP/SAVPF"?

Regards,
_____________
Roman Shpount