Subject: Re: [Sipping] Expert review of draft-ejzak-sipping-p-em-auth-00.txt

From: Gonzalo Camarillo <[email-masked]>
Date: Wed, 10 May 2006 14:44:49 +0300

Hi,

there have been plenty of discussions on whether or not what this draft 
is trying to do should be allowed or not. However, I do not see any 
discussions on the technical points below.

I would like to see the questions below answered to understand how you 
intend to use this mechanism. For example, the type of policies you can 
implement depend heavily on which means you intend to use to correlate 
early media with early dialogs and where you intend to stop unauthorized 
media. I believe that your answers will help us have a clearer 
understanding on the issues being discussed.

Thanks,

Gonzalo

Gonzalo Camarillo wrote:
> Hi,
> 
> some comments on the draft under discussion.
> 
> RFC 3960 points out a few issues related to forking and early media. 
> This draft should address them. For example, it should explain how user 
> agents are supposed to correlate a particular SIP early dialog with its 
> media packets. That is, how to distinguish between the early media sent 
> by two remote UASs and how to associate it with their respective SIP 
> dialogs.
> 
> Regarding which entity is authorized to send backward early media or 
> receive forward early media, this does not seem like a per dialog issue; 
> it seems more a per media stream issue. For example, if I have two media 
> streams (audio and video), the IVR in the network may be authorized to 
> send me backward early media (audio), but the UAS is not authorized to 
> send me anything. However, since both media streams (audio and video) 
> were established with the same SIP early dialog, the P-Early-Media 
> header field cannot provide this granularity. So, if early media is 
> authorized for this early dialog, the UAS will be able to send video... 
> the draft should discuss the granularity the solution should provide.
> 
> With respect to the policies the draft talks about, I do not think it is 
> necessary to spell them out. It would be better if the draft only talked 
> about early media that is authorized or unauthorized, and the mechanism 
> to achieve that distinction. Which types of early media a domain may 
> want or may not want to authorize (e.g., media from PSTN gateways vs. 
> media from UASs) can be left outside the scope of the draft.
> 
> Cheers,
> 
> Gonzalo

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