Re: [splices] Using Two Separate Devices to Start a Conversation proposal

Alan Johnston <alan.b.johnston@gmail.com> Mon, 06 June 2011 20:34 UTC

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Date: Mon, 6 Jun 2011 15:34:29 -0500
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From: Alan Johnston <alan.b.johnston@gmail.com>
To: Paul Kyzivat <pkyzivat@cisco.com>
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Subject: Re: [splices] Using Two Separate Devices to Start a Conversation proposal
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On Mon, Jun 6, 2011 at 2:48 PM, Paul Kyzivat <pkyzivat@cisco.com>; wrote:
>
>
> On 6/6/2011 3:35 PM, Alan Johnston wrote:
>>
>> If I understand correctly, there will be two separate RTP streams, two m=
>> lines?
>>
>> If this is the case, then two separate NAT traversal mechanisms will be
>> used (i.e. ICE rubs twice or two relays used). As far as ZRTP or other media
>> path keying protocols, each session will be keyed separately. With ZRTP the
>> endpoint will see two different ZIDs.  This does unfortunately mean two
>> Diffie Hellman calculations.
>>
>> Since these are separate sessions, each will have an RTCP session as well,
>> and these may need NAT traversal as well.
>>
>> So this will work, but things like logging and quality reporting will be
>> quite complicated.
>
> As Dale mentioned, this also depends on the other end doing the "right
> thing" with this case. It is a leap of faith to assume it will realize it
> should accept both streams and use one for input and the other for output.
>
> ISTM its at least as likely that it would accept the first stream, reject
> the second, and then have only a one-way "conversation".

OK, I understand the problem right now.  The problem is that this is a
special kind of "Join" operation.  It is kind of a join, but not
quite.

The operation we are after is perhaps similar to 3.3.8 Far-Fork in RFC 5850:

I suspect instead of Join, we need a new primitive, lets call it
Splice or Merge which requests the UAS to add the media in the INVITE
into the dialog that is referenced.

- Alan -

>
>        Thanks,
>        Paul
>
>> - Alan -
>>
>>
>>
>> On Jun 6, 2011, at 2:07 PM, "Worley, Dale R (Dale)"<dworley@avaya.com>;
>>  wrote:
>>
>>> ________________________________________
>>> From: splices-bounces@ietf.org [splices-bounces@ietf.org] On Behalf Of
>>> Peter Musgrave [musgravepj@gmail.com]
>>>
>>> I have concerns about this approach. Fundamentally the RTP stream is not
>>> symmetric (in the sense of RFC4961). This has consequences for NAT
>>> traversal, general interoperability and media path security schemes like
>>> ZRTP.
>>> _______________________________________________
>>>
>>> I have to agree and disagree...  As Rifaat diagrammed it, the call should
>>> work, as it uses already-defined SIP facilities.  Indeed, it's rather
>>> clever, I'd never thought of joining a sendonly dialog with a recvonly
>>> dialog.  There are some limitations, in that we depend on the far-end UA to
>>> execute the join in the way we want.
>>>
>>> The problems you raise, those of asymmetric RTP, already exist -- One can
>>> make a sendonly audio call, or a recvonly audio call.  We need to ensure
>>> that NAT traversal and ZRTP work correctly when  media stream is set up to
>>> be one-way.
>>>
>>> Dale
>>>
>>> _______________________________________________
>>> splices mailing list
>>> splices@ietf.org
>>> https://www.ietf.org/mailman/listinfo/splices
>>
>> _______________________________________________
>> splices mailing list
>> splices@ietf.org
>> https://www.ietf.org/mailman/listinfo/splices
>>
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