Subject: [rtcweb] JSEP: Usage of a=rtcp attribute

From: Christer Holmberg <[email-masked]>
Date: Sun, 13 Dec 2015 15:02:47 +0000

Hi,

Section 5.2.1 of draft-jsep contains the following statement:

   "o  An "a=rtcp" line, as specified in [RFC3605], Section 2.1,
      containing the dummy value "9 IN IP4 0.0.0.0", because no
      candidates have yet been gathered."

...i.e. the same port:address as in the associated c/m-line.

The problem is that the currently suggested mechanism to indicate exclusive support of RTP/RTCP-mux also says that the a=rtcp line shall be identical to the c/m-line.

My question is: is there really a need to always include the rtcp attribute in trickle offers? Isn't it enough to indicate port 9 in the m- line, and address 0.0.0.0 in the c-line? In my opinion that would also apply to RTCP.

Example:

JSEP trickle offer *without* mux-exclusive indication:

c=IN IP4 0.0.0.0
m=audio 9...
a=rtcp-mux

JSEP trickle offer *with* mux-exclusive indication:

c=IN IP4 0.0.0.0
m=audio 9...
              a=rtcp: 9 IN IP4 0.0.0.0
              a=rtcp-mux

Regards,

Christer