Re: [MMUSIC] WGLC on draft-ietf-mmusic-mux-exclusive-03.txt - change to draft-ice-sip-sdp

[Roman Shpount <[e-mail]>]

Hi Suhas,

I have previously proposed the following, which will remove rtcp attribute
if RTCP is not used. This will also cover mux exclusive case, since RTCP
candidates will not be present in such case:

On Tue, Jan 12, 2016 at 3:48 PM, Roman Shpount <[e-mail]> wrote:

> Cross-posting to MMUSIC, since this affects both RFC 5245bis and
> draft-ietf-mmusic-ice-sip-sdp
>
> RFC 5245 and draft-ietf-mmusic-ice-sip-sdp currently say the following:
>
>    The default candidates are added to the SDP as the default
>    destination for media.  For streams based on RTP, this is done by
>    placing the IP address and port of the RTP candidate into the c and m
>    lines, respectively.  *If the agent is utilizing RTCP, it MUST encode
>    the RTCP candidate using the a=rtcp attribute as defined in RFC 3605 <https://tools.ietf.org/html/rfc3605>
>    [RFC3605 <https://tools.ietf.org/html/rfc3605>].*  If RTCP is not in use, the agent MUST signal that using
>    b=RS:0 and b=RR:0 as defined in RFC 3556 <https://tools.ietf.org/html/rfc3556> [RFC3556 <https://tools.ietf.org/html/rfc3556>].
>
>
> There is an ongoing discussion whether the rtcp attribute is required in case of trickle ICE, when an offer is sent without candidate information, the RTP port set to 9, and the RTP IP address set to 0.0.0.0.
>
>
>
> Example:
>
>                               a=rtcp: 9 IN IP4 0.0.0.0
>
>
>
> According to Christer this is not needed, as there is no candidate to “encode”, and it also conflicts with the suggested mechanism for indicating exclusive support of RTP/RTCP multiplexing (draft-holmberg-mmusic-mux-exclusive).
>
>
> Furthermore, according to section 2.1 of RFC 3605:
>
>
>    The RTCP attribute is used to document the RTCP port used for media
>    stream, when that port is not the next higher (odd) port number
>    following the RTP port described in the media line.
>
>
> RFC 5245 overwrites the guideline from RFC 3605 and states that SDP rtcp
> attribute MUST be present even when RTCP default candidate is not present
> or when RTCP candidate is using port rtp+1, which is currently the the most
> common scenario since sequential port is typically allocated for RTCP by
> TURN.
>
> I suggest changing the language in section 4.2
> of draft-ietf-mmusic-ice-sip-sdp to:
>
>    The default candidates are added to the SDP as the default
>    destination for media.  For streams based on RTP, this is done by
>    placing the IP address and port of the RTP candidate into the c and m
>    lines, respectively.  *If the agent is utilizing RTCP and if RTCP *
>
> *   candidate is present and not equal to the same address and *
>
> *   the next higher port number of the RTP candidate, the agent MUST encode
>    the RTCP candidate using the a=rtcp attribute as defined in RFC 3605 <https://tools.ietf.org/html/rfc3605>
>    [RFC3605 <https://tools.ietf.org/html/rfc3605>].*  If RTCP is not in use, the agent MUST signal that using
>    b=RS:0 and b=RR:0 as defined in RFC 3556 <https://tools.ietf.org/html/rfc3556> [RFC3556 <https://tools.ietf.org/html/rfc3556>].
>
>
>
_____________
Roman Shpount

On Tue, Mar 1, 2016 at 11:31 AM, Christer Holmberg <
[e-mail]> wrote:

> Hi Suhas,
>
> ...
>
> >>> Note that again, this is a box of our own design, we can decide to
> update those documents here.  "The a=rtcp attribute MUST NOT be included
> >>>unless other documents (other than RFC 5761) mandate its inclusion.  If
> present, a=rtcp MUST include a port number of 9."  Or something along those
> lines.
> >>
> >> Sure, I can add text like that to the draft, and we can update
> ice-sip-sdp.
> >
> > [Suhas] .. What are the specific updates for ice-sip-sdp. Sorry if i
> have missed the context. I am happy to consider the inputs for these
> updates if I get to know the concrete updates.
>
> ice-sip-sdp requires usage of a=rtcp if RTCP is used. My suggestion is to
> remove that requirement if mux-exclusive is used.
>
> Regards,
>
> Christer
>
>
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