Subject: [MMUSIC] Handling the transport protocol and default candidate in the answer

From: Roman Shpount <[email-masked]>
Date: Fri, 26 Apr 2019 16:58:52 -0400

Hi All,

One more change regarding the
https://github.com/suhasHere/ice-sip-sdp/pull/1

 There is one scenario which was not well covered in ice-sip-sdp which was
described in JSEP.

Imagine end point receives an offer which contains both UDP and TCP
candidates. Default candidate for this offer is set to TCP based transport.
Answering end point only contains UDP based candidates.

There are two questions:

1. What transport protocol should the answering end point put in the m=
line?
2. What address and port should answering end point put in c= and m= line
as a default destination?

My suggestion is that answering end point should put the same transport
protocol in the answer as was specified in the offer. Since none of the
candidates match the transport protocol in the m= line, end point should
use dummy address "0.0.0.0"/"::" and port value of "9". This should also
prevent the ICE mismatch during the answer handling that could otherwise
cause answer handling according to RFC 3264 rules.

In order to specify this I have added the following note to Sending the
Initial Answer section:

NOTE: In each "m=" line, the answerer MUST use the same transport protocol
as was used in the offer "m=" line. If none of the candidates in the "m="
line in the answer use the same transport protocol as indicated in the
offer "m=" line, then, in order to avoid ICE mismatch, default destination
should be set to IP address values "0.0.0.0"/"::" and port value of "9".

Please let me know what you think.
_____________
Roman Shpount