Subject: Re: [Sip] GRUU and Mid-Dialog Requests

From: "Xavier Marjou" <[email-masked]>
Date: Fri, 25 Aug 2006 16:28:53 +0200

> That doesn't solve the use cases that GRUU was devised for.

> The interesting cases are when UA X has registered at an AOR 
> (lets call it AOR-X) that has multiple registered contacts. 
> When UA X answers a dialog establishing request to AOR-X, 
> it needs to put something in the Contact address - something 
> that will route back to it.

> I suppose, following your proposal, when it receives such a request 
> it could but its gruu into the Contact of the response. But in that 
> case we have all the same issues as the current proposal.

Let's say UA X has a regular AOR (AOR-X), and 2 GRUU AOR (AOR-X;gruu=111 
and AOR-X;gruu=222).
When registering from device1, he both both AOR-X and AOR-X;gruu=111
When registering from device2, he both both AOR-X and AOR-X;gruu=222

When UA X answers a call on device1, it updates the addr in the "To" header 
with its GRUU AOR (AOR-X;gruu=111), but it does not modify the remote-
target (Contact). Then the remote peer can use this GRUU-AOR to send a 
SUBSCRIBE for example. Of course, I know this breaks what has been 
envisioned for so far that is to advertise the GRUU in the remote-target.

> So you are defining the term "GRUU AOR" to mean an AOR 
> that only accepts on registered contact.

Yes, the idea would be to register the regular AOR from all devices (as 
usual many addr of contact are allowed) and to also regiter one derived 
AOR-GRUU per device (for each AOR-GRUU, only one addr of contact is 
allowed).

> I think I must be missing something key in what you are proposing. 
> It seems like you are simply suggesting that all problems go away 
> if we never allow more than one contact to be registered with an AOR.

I would certainly not pretend that "all the problems go away" for this 
complex topic ;-) I know I may not be aware of the whole story nor of all 
the possible impacts. Just consider it as an alternative I suggest to 
investigate.

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From: Paul Kyzivat <[email-masked]>
Date: Fri, 25 Aug 2006 11:59:24 -0400

> Let's say UA X has a regular AOR (AOR-X), and 2 GRUU AOR (AOR-X;gruu=111 

The above is a little confusing, because I had assumed "UA X" referred 
to a user agent, but the way you are using it it seems to refer to a 
user with two user agents (devices). But now that I see how you are 
using the terms I can manage for now.

> target (Contact).

I'm not sure what you are suggesting here. Updating the To header is 
currently not allowed.

There have been some suggestions to permit it to be changed in a 
subsequent UPDATE request. Is that what you have in mind?

It would be helpful if you would send an example, containing the 
messages and headers that you propose using.

> Then the remote peer can use this GRUU-AOR to send a 

Ignoring the details, this is similar to a proposal long ago to carry 
the gruu in a new header, rather than in the Contact header. That was 
abandoned because it would require changes in previously conforming 
implementations to work with UAs conforming to gruu.

Maybe what you have in mind will have a new twist. If you want, send out 
something with more detail. BUT, the gruu proposal has been baking for a 
long time, so this is kind of late to consider a major change.

	Paul