Re: [rtcweb] No Plan

Christer Holmberg <christer.holmberg@ericsson.com> Tue, 04 June 2013 14:11 UTC

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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>, Emil Ivov <emcho@jitsi.org>
Thread-Topic: [rtcweb] No Plan
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Date: Tue, 4 Jun 2013 12:35:10 +0000
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Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] No Plan
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Hi,

>> 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.
>
> I now think that it is enough like plan B that the two should be collapsed together. Make the signaling of the explicit SSRCs optional when there is some other mechanism to agree upon them.

When you say "signaling", do you refer to what is sent on the wire?

As others have said, we still need API support to control things - no matter whether it's done using SDP or some other mechanism.

Regards,

Christer


>> 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
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>>>> rtcweb mailing list
>>>> rtcweb@ietf.org
>>>> https://www.ietf.org/mailman/listinfo/rtcweb
>>>> .
>>>>
>>>
>>> --
>>> https://jitsi.org
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>>> rtcweb@ietf.org
>>> https://www.ietf.org/mailman/listinfo/rtcweb
>>>
>>
>> _______________________________________________
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>> rtcweb@ietf.org
>> https://www.ietf.org/mailman/listinfo/rtcweb
>>
>

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