Subject: [Sip] GRUU and grid

From: Eric Rescorla <[email-masked]>
Date: Mon, 18 Sep 2006 14:51:49 -0700

I recently made another pass through gruu-10 and I started wondering
about the use of the "grid" parameter. ISTM that it serves two
purposes:

1. To let a UA hang a context variable/indicator off of a URI.
2. To let a UA know it was referenced via a GRUU.

So, the grid is sort of doing double duty in two not terribly
related contexts. That's not always bad, but I fear it is
in this case.

First, wouldn't it be nice to be able to hang a context
variable/indicator off any URI, not just a GRUU?  I've seen this issue
come up in the context of e-mail spam, where users would like to be able
to mint new e-mail addresses (sort-of capabilities) for each use to
enable easy filtering.  It's obviously really nice to be able to do this
without the help of your service provider. If you could use grids
(probably renamed) with AORs or something like them, that would work for
this, right? 

Second, just from an evocative perspective, having a "grid" parameter
which can get into the To: one of two ways and which means 
"I was referenced via a GRUU" feels overloaded. Why not invent
a different parameter for "I was referenced via a GRUU".

-Ekr

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---

From: Paul Kyzivat <[email-masked]>
Date: Tue, 19 Sep 2006 09:56:17 -0400

> related contexts. That's not always bad, but I fear it is

I must admit that this double usage arose out of expediency, and fairly 
recently.

Originally there was no way to tell whether you had been invoked via a 
gruu or the corresponding AOR, except if you had happened to use a grid 
parameter and it hadn't been tampered with. But that turned out not to 
be good enough.

The usage seemed benign enough at the time.

> variable/indicator off any URI, not just a GRUU? 

Perhaps. Though the logistics get more difficult. If the context is 
applied to an AOR, and can be delivered to multiple UAs, then they must 
have a common agreement about the meaning of the context. But I suppose 
somebody would find a use for it.

> I've seen this issue
> which can get into the To: one of two ways

It is only the R-URI that can get a grid parameter in two ways.

> and which means 

I think of the grid parameter with no value as simply the "default" 
value in a gruu, so it doesn't feel overloaded to me.

Would it seem less weird if the gruu that was returned by the registrar 
was pre-populated with a grid parameter with no value? (And the 
understanding that the UA may add a value to it if desired.) In that 
case, the use of a gruu with no grid parameter would be an error, which 
could be fixed either by rejecting it or by inserting the grid parameter.

But I also don't have a big problem with making this two parameters if 
there is agreement that grid should be usable for non-gruus. The 
downside to this is that the grid parameter requires special action from 
the proxy translating the R-URI. Coupling this to gruu ensures it will 
be implemented where it needs to be. If it were decoupled then I don't 
know how you ensure the proper translation will be done.

	Paul