Re: [Sip] draft-ietf-sip-gruu-10 comments

[Paul Kyzivat <pkyzivat at cisco.com>]

Cullen Jennings wrote:

> Section 8.2.2
>
> I think I am likely confused here. I basically don't see why a simple 
> classic sip trapezoid deployment would ever need to Record Route. The 
> fact that the GRUU refereed to the "home" domain would cause it work get 
> back here. As a side note, I find the terms "home", "edge" etc very 
> undefined outside the IMS context. Anyways, I believe this section might 
> be all right but I am failing to understand what needs to be done and 
> why. If I was a non IMS proxy implementer, I suspect I would just ignore 
> this whole section.

*If* the topology is a simple trapezoid then I think you are correct.

But if there is a proxy before the originating home proxy, or after the 
terminating home proxy, then the R-R is needed to prevent a spiral.

On the originating side, this can be determined by whether there is a 
R-R present when the request arrives at the originating home proxy. On 
the terminating side that doesn't work, because the potential R-R hasn't 
happened yet, and you can't know in advance if it will happen.

So the problem is that you don't need it in a trapezoid, but you don't 
know if you have a trapezoid.

	Paul

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