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Re: [rtcweb] BUNDLE with implicit rtcp-mux

Christer Holmberg <christer.holmberg@ericsson.com> Fri, 14 March 2014 05:56 UTC

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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: Justin Uberti <juberti@google.com>
Thread-Topic: [rtcweb] BUNDLE with implicit rtcp-mux
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Date: Fri, 14 Mar 2014 05:56:38 +0000
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Subject: Re: [rtcweb] BUNDLE with implicit rtcp-mux
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Hi,

Just to clarify: you would still use the a=rtcp-mux attribute, right?

It is e.g. needed to inform intermediaries (that may not understand BUNDLE) about the usage of RTCP mux.

Regards,

Christer

Sent from my Sony Ericsson Xperia arc S

Justin Uberti <juberti@google.com> wrote:





On Thu, Mar 13, 2014 at 5:52 AM, Christer Holmberg <christer.holmberg@ericsson.com<mailto:christer.holmberg@ericsson.com>> wrote:
Hi Justin,

> I think rtcp-mux has to be a MUST use when BUNDLE is used between the two endpoints. (If the endpoint doesn't support
> BUNDLE, rtcp-mux is not required.)
>
> Otherwise, you get into weird edge cases, such as where you have a data channel (no RTCP component), and then want
> to add audio (with RTP and RTCP components). You could bundle the audio RTP over the existing data channel transport,
> but it's not clear what you should do with the RTCP component. Mandating rtcp-mux avoids this issue completely.

According to section 4 in RFC 5761, if you multiplex RTP and RTCP on the same port, you need to assign dedicated PT values to the RTCP packets, which means that at least PT values 64-95 cannot be used for RTP.

As you have been one of those talking about the risk of running out of PT values, I just want to make sure you have taken this into consideration :)


Yes. The upside of rtcp-mux far outweighs this minor limitation.

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