[rtcweb] Default proto transport in JSEP

[Roman Shpount <[e-mail]>]

Hi All,

The current language in JSEP makes it incompatible with any ICE
implementation, either existing or the future ones compliant with
ice-sip-sdp draft. You can, of course, overwrite ice-sip-sdp, but this will
mean JSEP will be a completely incompatible system.

The problem is that JSEP proposes to use UDP protocol in the m= line and at
the same time update address and port to the currently selected candidate.
Based on ice-sip-sdp, if protocol of the current selected candidate does
not match protocol in the m= line, this will mean either ICE mismatch or
additional candidate with protocol, address, and port form m= and c= line.

Second, ice-sip-sdp treats SDP during ICE restart, when multiple candidates
are present different from SDP when ICE is not restarted (single
candidate). According to ice-sip-sdp, when only a single candidate is
present, this candidate protocol, address and port are set in m= and c=
line. JSEP proposes to put original UDP protocol and address and port from
the single candidate.

To be specific, it is not the fact that protocol in m= line is not updated
is an issue. It is that protocol in not updated but address and port in m=
and c= line are updated. In the ice-sip-sdp draft there is a solution for
this issue -- set address to IN IP4 0.0.0.0 and port to 9. This is
specifically supposed to be ignored and not cause the ICE mismatch or extra
candidates. If JSEP wants to overwrite ice-sip-sdp, it can specify that m-
line protocol should always be set to UDP based protocol, c= line address
should be set to   IN IP4 0.0.0.0 and m= line port set to 9. In case of an
ICE only system where c= and m= line address information is irrelevant,
this makes implementation simpler since m= and c= line address information
can stay constant for the duration of the session.

Regards,
_____________
Roman Shpount