Re: [rtcweb] No Plan

Emil Ivov <emcho@jitsi.org> Mon, 03 June 2013 21:44 UTC

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Date: Tue, 04 Jun 2013 00:41:44 +0300
From: Emil Ivov <emcho@jitsi.org>
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To: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: Re: [rtcweb] No Plan
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On 03.06.13, 23:40, Paul Kyzivat wrote:
> +1
>
> The more we dig into this the more it looks like Plan B.

I am not sure exactly what you mean by this. I did try to make it clear 
that "No Plan" has a lot in common with "Plan B". The main differences 
are that there is no expectation for SSRCs to be pre-announced and there 
are requirements for WebRTC APIs to provide the tools necessary for apps 
to control individual streams themselves.

Emil

>
> 	Thanks,
> 	Paul
>
> On 6/1/13 7:05 AM, Christer Holmberg wrote:
>>
>> Hi,
>>
>>>> The draft says:
>>>>
>>>>         "For the sake of interoperability this specification strongly advises
>>>>         against the use of multiple m= lines for a single media type."
>>>
>>> This should probably be clarified. The above referred mostly to a
>>> browser's expectations and default offers. Multiple m= lines can confuse
>>> a number of existing legacy endpoints which is why they should be
>>> avoided when initiating a session that could reach a similar device (and
>>> by default this should be assumed for any session).
>>>
>>> If applications *know* that they need to have multiple m= lines of a
>>> given type they can request this the same way they could do it with Plan B:
>>>
>>>      If the application wishes, it can request that a given
>>>      media source be placed onto a separate m= line, by setting a new
>>>      .content property on the desired MediaStreamTrack; the values for the
>>>      .content property are those defined for the a=content attribute in
>>>      [RFC4796].
>>>
>>> I'll make sure this is part of the next version.
>>>
>>> Does this make sense?
>>
>> I have nothing against a general recommendation to, for a given media type, have as few m- lines as possible.
>>
>> But, I do think the draft need to point out that it is not always possible, e.g. because:
>>
>> 1) m- lines have different characteristics (normally indicated using SDP attributes) that does not "fit" all content for the given media type;
>> 2) different protocols are used for different m- lines, even if the media type is the same; or
>> 3) the remote endpoint only supports a single (or, another given number) of sources per m- line.
>>
>> Etc.
>>
>> Regards,
>>
>> Christer
>>
>>
>>
>>
>>
>>> My understanding is that the usage of multiple m= lines for a single media type would not affect the mechanism as such, but I just want to verify that :)
>>>
>>> Also, there ARE "legacy" implementations that use multiple m= lines for a single media type (e.g. video enabled devices using two video m= lines: one for camera content, and one for slides).
>>>
>>> So, while I definitely think that legacy interoperability shall be taken into consideration, I would not like to make such strong statements. In my opinion (the draft also talks about it), the usage of multiple simultaneous SSRCs per m- line is a much bigger issue when it comes to legacy interoperability.
>>>
>>> Also, in CLUE we have been working on signaling scenarios with multiple m= lines per media type.
>>    >
>>>
>>> Regards,
>>>
>>> Christer
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: rtcweb-bounces@ietf.org [mailto:rtcweb-bounces@ietf.org] On Behalf Of Emil Ivov
>>> Sent: 29. toukokuuta 2013 22:00
>>> To: rtcweb@ietf.org
>>> Subject: [rtcweb] No Plan
>>>
>>> Hey all,
>>>
>>> Based on many of the discussions that we've had here, as well as many others that we've had offlist, it seemed like a good idea to investigate a negotiation alternative that relies on SDP and Offer/Answer just a little bit less.
>>>
>>> The following "no plan" draft attempts to present one such approach:
>>>
>>> http://tools.ietf.org/html/draft-ivov-rtcweb-noplan
>>>
>>> The draft relies on conventional use of SDP O/A but leaves the intricacies of multi-source scenarios to application-specific signalling, with potentially a little help from RTP.
>>>
>>> Hopefully, proponents of Plans A and B would find that the interoperability requirements that concerned them can still be met with "no plan". Of course they would have to be addressed by application-specific signalling and/or signalling gateways.
>>>
>>> Comments are welcome!
>>>
>>> Cheers,
>>> Emil
>>>
>>> --
>>> https://jitsi.org
>>> _______________________________________________
>>> rtcweb mailing list
>>> rtcweb@ietf.org
>>> https://www.ietf.org/mailman/listinfo/rtcweb
>>> .
>>>
>>
>> --
>> https://jitsi.org
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>>
>
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