Re: [MMUSIC] BUNDLE and RTCP

Christer Holmberg <christer.holmberg@ericsson.com> Mon, 19 October 2015 16:40 UTC

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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>, "mmusic@ietf.org" <mmusic@ietf.org>
Thread-Topic: [MMUSIC] BUNDLE and RTCP
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Date: Mon, 19 Oct 2015 16:40:43 +0000
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Subject: Re: [MMUSIC] BUNDLE and RTCP
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Hi,

> Good discussion.
>
> How about the following:
>
> If there is an RTP m-line in the bundle, and rtcp-mux is *not* negotiated, then the rtcp port is determined according to the rules
> for the first m-line selected in the bundle group. If *that* line has, and allows, an a=rtcp, then that is used. If that line doesn't have 
> a=rtcp, then port+1 is used, even if this isn't an rtp m-line.

Sure. But, as the offerer doesn't know for sure which m- line will be selected, it always has to be prepared to use port+1, so why not use port+1 to begin with? 

I guess my question is whether someone really needs a=rtcp with BUNDLE? As far as I know, most current implementations do rtcp-mux, and for those that don't/can't there is always port+1. 

> (Right now there isn't any way to have a bundle group with more than one non-rtp m-line, but that might not always be so.)

Correct.

Regards,

Christer



On 10/19/15 3:35 AM, Christer Holmberg wrote:
> Hi,
>
> ...
>
> ...
>
> ...
>
>     HOWEVER, we could make it SIMPLE and either:
>
>     1)*Mandate usage of rtcp-mux with BUNDLE*. I.e. if BUNDLE is
>     negotiated, rtcp-mux MUST be used.
>
>     This was already suggested in the past, but Paul(?) said we should
>     not make such restriction without a good reason. I think the current
>     issue is a good reason :)
>
>     m=data channel 10000
>
>     m=rtp 11111
>
>     a=rtcp-mux
>
>     m=rtp 11222
>
>     a=rtcp-mux
>
>     2)*Mandate usage of either rtcp-mux OR the default "+1" port with
>     BUNDLE*. I.e. if BUNDLE is negotiated, rtcp-mux or "+1" MUST be
>     used. The selection is based on whether the rtcp-mux attribute was
>     included in the offer/answer or not.
>
>     m=data channel 10000             // rtcp-mux
>
>     m=rtp 11111
>
>     a=rtcp-mux
>
>     m=rtp 11222
>
>     a=rtcp-mux
>
>     m=data channel 10000             // "+1"
>
>     m=rtp 11111
>
>     m=rtp 11222
>
>     The solutions above would not allow explicit negotiation of an RTCP
>     port when BUNDLE is used, but maybe we could live with that?
>
>>Well, I could live with both of your suggestions, but I thought you
> wanted a solution that can also negotiate which a=rtcp attribute to use.
>
>>If nobody really needs something like that , I would prefer 1) as it
> removes the needs for several implementation option that would only be 
> needed to cover full backwards compatibility but would hardly be used.
>
> Personally I don't have a strong preference, but as far as I know 
> there may be environments where separate ports for RTP and RTCP are 
> desired - even if BUNDLE is used.
>
>>>Now, if we can agree on a way forward before Yokohama, you won't have 
>>>to
> sit listening to me talking about BUNDLE at the meeting :)
>>
>>Well, I wouldn't be sitting there anyhow but understand that your
> motivation to speak there about BUNDLE again is probably limited.
>
> I don't mind talking about BUNDLE - but I'd like to talk about it in 
> the context of the great RFC that we have published :)
>
> Regards,
>
> Christer
>
>
>
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