Re: [rtcweb] Multiplexing using the same port number for multiple media descritions

Justin Uberti <juberti@google.com> Tue, 30 August 2011 14:40 UTC

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From: Justin Uberti <juberti@google.com>
Date: Tue, 30 Aug 2011 10:41:57 -0400
Message-ID: <CAOJ7v-0uX6mGwExqW_+==UN0c_GVxU22k=uuVsMcPb=j1mhvtA@mail.gmail.com>
To: Christer Holmberg <christer.holmberg@ericsson.com>
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Subject: Re: [rtcweb] Multiplexing using the same port number for multiple media descritions
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I think Harald's approach is cleaner, since the fallback does not require a
new offer. What do you see as problematic with Harald's suggestion?

On Tue, Aug 30, 2011 at 7:21 AM, Christer Holmberg <
christer.holmberg@ericsson.com> wrote:

>  Hi,
>
> One possible alternative solution for SDP multiplex negotiation could be
> based on the assumption of using the same port number in multiple SDP m-
> lines (yes, I know SDP does not allow it, and I will come back to that).
>
> Something like:
>
> SDP offer:
>
> m=audio 10000 ...
> a=rtpmap ...
> a=rtpmap ...
> m=video 10000 ...
> a=rtpmap ...
> a=rtpmap ...
>
>
> SDP answer (multiplex supported/accepted):
>
> m=audio 20000 ...
> a=rtpmap ...
> a=rtpmap ...
> m=video 20000 ...
> a=rtpmap ...
> a=rtpmap ...
>
>
> SDP answer (multiplex not-supported/rejected):
>
> m=audio 20000 ...
> a=rtpmap ...
> a=rtpmap ...
> m=video 30000 ...
> a=rtpmap ...
> a=rtpmap ...
>
>
>
> MAYBE there is also a need to use some kind of grouping, in which case it
> could look something like (borrowing some terminology from Harald):
>
>
>
> SDP offer:
>
> a=group:TOGETHER foo bar
> m=audio 10000 ...
> a=mid:foo
> a=rtpmap ...
> a=rtpmap ...
> m=video 10000 ...
> a=mid:bar
> a=rtpmap ...
> a=rtpmap ...
>
>
> SDP answer (multiplex supported/accepted):
>
> m=audio 20000 ...
> a=rtpmap ...
> a=rtpmap ...
> a=mid:foo
> m=video 20000 ...
> a=mid:bar
> a=rtpmap ...
> a=rtpmap ...
>
>
> SDP answer (multiplex not-supported/rejected):
>
> m=audio 20000 ...
> a=rtpmap ...
> a=rtpmap ...
> m=video 30000 ...
> a=rtpmap ...
> a=rtpmap ...
>
>
> An ISSUE with this solution is of course that SDP does not allow for it.
>
> However, we could always say that browsers must support it, in which case
> it should work fine in direct browser-to-browser cases.
>
>
> When interworking with legacy, I guess two things can happen:
>
> 1. The offer is acctepted, with different port number in the answer, and
> multiplex won't be used (see example above)
>
> 2. The offer is rejected. In this case, the fallback would be that the
> browser sends a new offer, with different port numbers, and multiplex won't
> be used.
>
> Regards,
>
> Christer
>
>
>
>
> _______________________________________________
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> https://www.ietf.org/mailman/listinfo/rtcweb
>
>