Re: [AVTCORE] RTP/RTCP-mux: Attribute in answer if not included in offer?

Den 2016-05-30 kl. 10:08, skrev Christer Holmberg:
> Hi Suhas,
>
> I have the same understanding as you: the offerer indicates support of
> RTP/RTCP-mux, and the answerer decides whether to use it or not. And, if
> used, it will be used in BOTH directions – i.e. the usage of RTP/RTCP is
> not per direction.
>
> Colin? Magnus?

Yes, I do agree with your interpretations here. Both that it applies 
bi-directional after mutual agreement, and that if the answer would like 
to use it, it will have to do a re-invite with an offer including 
a=rtcp-mux attribute to see if the peer accepts that.

/Magnus

>
> Regards,
>
> Christer
>
> From: Suhas Nandakumar <suhasietf@gmail.com <mailto:suhasietf@gmail.com>>
> Date: Friday 27 May 2016 at 04:25
> To: Christer Holmberg <christer.holmberg@ericsson.com
> <mailto:christer.holmberg@ericsson.com>>
> Cc: "mmusic@ietf.org <mailto:mmusic@ietf.org>" <mmusic@ietf.org
> <mailto:mmusic@ietf.org>>, "avt@ietf.org <mailto:avt@ietf.org>"
> <avt@ietf.org <mailto:avt@ietf.org>>, Magnus Westerlund
> <magnus.westerlund@ericsson.com
> <mailto:magnus.westerlund@ericsson.com>>, Colin Perkins
> <csp@csperkins.org <mailto:csp@csperkins.org>>
> Subject: Re: [AVTCORE] RTP/RTCP-mux: Attribute in answer if not included
> in offer?
>
> Going along O/A negotiation procedures, i would lean towards your former
> conclusion that the offer needs to include the rtcp-mux ability.
> If the offer doesn't include a=rtcp-mux and the answerer wants to mux ,
> then it needs a new O/A from the answerer's perspectives.
>
>
> If we make a=rtcp-mux a declarative SDP it might solve the other use-case ..
>
> thanks
> Suhas
>
> On Thu, May 26, 2016 at 1:01 PM, Christer Holmberg
> <christer.holmberg@ericsson.com <mailto:christer.holmberg@ericsson.com>>
> wrote:
>
>     (Sorry for the cross-posting)____
>
>     __ __
>
>     Hi,____
>
>     __ __
>
>     There has been a discussion in 3GPP regarding RFC 5761
>     (RTP/RTCP-mux).____
>
>     __ __
>
>     Section 5.1.1 says:____
>
>     __ __
>
>     5.1.1.  SDP Signalling____
>
>     __ __
>
>        When the Session Description Protocol (SDP) [8] is used to
>     negotiate____
>
>        RTP sessions following the offer/answer model [9], the
>     "a=rtcp-mux"____
>
>        attribute (see Section 8) indicates the desire to multiplex RTP
>     and____
>
>        RTCP onto a single port.  The initial SDP offer MUST include this____
>
>        attribute at the media level to request multiplexing of RTP and
>     RTCP____
>
>        on a single port.  For example:____
>
>     __ __
>
>            v=0____
>
>            o=csp 1153134164 1153134164 IN IP6
>     2001:DB8::211:24ff:fea3:7a2e____
>
>            s=-____
>
>            c=IN IP6 2001:DB8::211:24ff:fea3:7a2e____
>
>            t=1153134164 1153137764____
>
>            m=audio 49170 RTP/AVP 97____
>
>            a=rtpmap:97 iLBC/8000____
>
>            a=rtcp-mux____
>
>     __ __
>
>        This offer denotes a unicast voice-over-IP session using the
>     RTP/AVP____
>
>        profile with iLBC coding.  The answerer is requested to send both
>     RTP____
>
>        and RTCP to port 49170 on IPv6 address
>     2001:DB8::211:24ff:fea3:7a2e.____
>
>     __ __
>
>        If the answerer wishes to multiplex RTP and RTCP onto a single
>     port,____
>
>        it MUST include a media-level "a=rtcp-mux" attribute in the
>     answer.____
>
>        The RTP payload types used in the answer MUST conform to the
>     rules in____
>
>        Section 4.____
>
>     __ __
>
>        If the answer does not contain an "a=rtcp-mux" attribute, the
>     offerer____
>
>        MUST NOT multiplex RTP and RTCP packets on a single port.
>     Instead,____
>
>        it should send and receive RTCP on a port allocated according to
>     the____
>
>        usual port-selection rules (either the port pair, or a signalled
>     port____
>
>        if the "a=rtcp:" attribute [10] is also included).  This will
>     occur____
>
>        when talking to a peer that does not understand the "a=rtcp-mux"____
>
>        attribute.____
>
>     __ __
>
>     Q: The question is whether it is allowed to include a=rtcp-mux in an
>     answer if the associated offer did NOT contain a=rtcp-mux.____
>
>     __ __
>
>     The second last paragraph in the text above does say that, if the
>     answer wishes to do RTP/RTCP-mux, it includes a=rtcp-mux in the
>     answer.____
>
>     __ __
>
>     BUT, in my view that is it based on the first paragraph, which
>     assumes a=rtcp-mux is also included in the offer.____
>
>     __ __
>
>     Or, am I wrong? Is it allowed to include a=rtcp-mux in the answer,
>     even if it’s not included in the offer? If so, how will the offerer
>     then indicate whether mux is used or not.____
>
>     __ __
>
>     Regards,____
>
>     __ __
>
>     Christer____
>
>     __ __
>
>
>     _______________________________________________
>     Audio/Video Transport Core Maintenance
>     avt@ietf.org <mailto:avt@ietf.org>
>     https://www.ietf.org/mailman/listinfo/avt
>
>

-- 

Magnus Westerlund

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