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Re: [rtcweb] Does RID require the same ext id for all the m= sections?

"Mo Zanaty (mzanaty)" <mzanaty@cisco.com> Mon, 11 September 2017 15:02 UTC

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From: "Mo Zanaty (mzanaty)" <mzanaty@cisco.com>
To: Iñaki Baz Castillo <ibc@aliax.net>
CC: "rtcweb@ietf.org" <rtcweb@ietf.org>
Thread-Topic: [rtcweb] Does RID require the same ext id for all the m= sections?
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Date: Mon, 11 Sep 2017 15:02:36 +0000
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Subject: Re: [rtcweb] Does RID require the same ext id for all the m= sections?
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Bundle defines MID, and section 13 restricts all extmap IDs (including MID, RID, etc.) to be consistent across all bundled m= sections, just like PTs. I see no restriction against aliases, nor any reason to impose one.

Mo

From: Iñaki Baz Castillo <ibc@aliax.net<mailto:ibc@aliax.net>>
Date: Monday, September 11, 2017 at 9:52 AM
To: mzanaty <mzanaty@cisco.com<mailto:mzanaty@cisco.com>>
Cc: "rtcweb@ietf.org<mailto:rtcweb@ietf.org>" <rtcweb@ietf.org<mailto:rtcweb@ietf.org>>
Subject: Re: [rtcweb] Does RID require the same ext id for all the m= sections?

Ok, but that is not valid for MID, as the reveiver transport is supposed to check the MID value using a single extmap ID, right?

El 11 sept. 2017 3:34 p. m., "Mo Zanaty (mzanaty)" <mzanaty@cisco.com<mailto:mzanaty@cisco.com>> escribió:
See bundle section 13.

https://tools.ietf.org/html/draft-ietf-mmusic-sdp-bundle-negotiation-38#section-13

The same ID must always map to the same URN. Different IDs can map to the same URN as aliases. (The latter is not stated but implied.)

Mo

On Sep 11, 2017, at 8:49 AM, Iñaki Baz Castillo <ibc@aliax.net<mailto:ibc@aliax.net>> wrote:

On Sun, Sep 10, 2017 at 8:22 PM, Mo Zanaty (mzanaty) <mzanaty@cisco.com<mailto:mzanaty@cisco.com>> wrote:
All extmap IDs must be consistent in all bundled m= sections, just like PTs.

Thanks.

However, what does "consistent" mean? I assume/expect that the extmap
ID (for example a=extmap:4) cannot exist in two different m= sections
pointing to different extension URLs, right?

But, and given that you told about PTs, it's perfectly valid that two
different PTs point to the same codec+condiguration within the same m=
section or in different m= sections.

So, could a m=audio section have an "a=extmap:4 urn:foo" line while a
m=video section has "a=extmap:8 urn:foo"? or should both use extmap ID
4?

For example, the extmap ID for MID must be *UNIQUE* across all the
m=sections. Does the same constrain exist for the extmap ID for RID?



--
Iñaki Baz Castillo
<ibc@aliax.net<mailto:ibc@aliax.net>>

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