Re: [MMUSIC] BUNDLE and separate RTP and RTCP ports even when rtcp-mux is used

["Muthu Arul Mozhi Perumal (mperumal)" <[e-mail]>]

Hi Christer,

I think the question boils down to whether the fallback port for RTCP described in section 5.1.3 of RFC5761 could be the same as the RTP port. This looks fine from a pragmatic point of view. However, the following statements from RFC5761 seem to forbid it:

   On receipt of the answer, the offerer looks for the presence of the
   "a=rtcp-mux" line for each media where multiplexing was offered.  If
   this is present, then connectivity checks proceed as if only a single
   candidate (for RTP) were offered, and multiplexing is used once the
   session is established.  If the "a=rtcp-mux" line is not present, the
   session proceeds with connectivity checks using both RTP and RTCP
   candidates, eventually leading to a session being established with
   RTP and RTCP on separate ports (as signalled by the "a=rtcp:"
   attribute).

Not sure if the statement "eventually leading to a session being established with RTP and RTCP on separate ports" was intentional. If not, it needs to be fixed.

Muthu

|-----Original Message-----
|From: [e-mail] [mailto:[e-mail]] On Behalf Of Christer Holmberg
|Sent: Thursday, July 05, 2012 3:39 AM
|To: [e-mail]
|Subject: [MMUSIC] BUNDLE and separate RTP and RTCP ports even when rtcp-mux is used
|
|Hi,
|
|A question related to RTP/RTCP multiplexing with BUNDLE.
|
|BUNDLE allows the usage of identical port numbers for multiple m- lines. It also
|expects a remote endpoint that does not support BUNDLE to send media associated
|with multiple m- lines to that single port, even if the remote endpoint itself will use
|different ports for each m- line.
|
|In addition, the BUNDLE client can also multiplex RTP and RTCP, using the a=rtcp-mux attribute.
|
|However, RFC 5761 says that one must be able to receive RTCP on the default RTCP port,
|if the remote endpoint does not support a=rtcp-mux attribute.
|
|But, even if the remote endpoint does not support RTCP/RTP muxing, the question is whether
|the local endpoint could still use the same port for RTCP/RTP - and expect the remote endpoint
|to send both RTP and RTCP to that single port (even if the remote endpoint itself uses different
|ports for RTP and RTCP). In addition to the a=rtcp-mux attribute, the local endpoint
|would use the a=rtcp attribute, containing the RTP port value.
|
|That would also, when ICE is used, prevent the local endpoint from having to reserve
|RTCP specific candidate ports.
|
|Regards,
|
|Christer
|_______________________________________________
|mmusic mailing list
|[e-mail]
|https://www.ietf.org/mailman/listinfo/mmusic