Re: [Sip] When does the registrar have to create GRUUs ?

[Paul Kyzivat <[e-mail]>]

[e-mail] wrote:
> Hi Jonathan,
> 
> GRUU draft tells the registrar to create a public GRUU and a
> temporary GRUU whenever it receives a REGISTER request with
> "+sip.instance" Contact header parameter but only return
> them is the REGISTER request contains Supported: gruu.
> 
> Does this make any sense ? Why would the registrar have to
> create those GRUUs if it would not return them to the UA ?
> 
> The use case I am thinking is:
> 
> - A registrar which supports both GRUU and Outbound 
> - An UA which supports Outbound but not GRUU
> 
> Such an UA would send its Contact header with "+sip.instance"
> parameter but it would not include Supported: gruu in its
> REGISTER. Strictly speaking GRUU draft currently tells
> the registrar to create GRUUs but not to return them to 
> the UA.
> 
> I would assume GRUU draft needs a small fix to tell the
> registrar to create the GRUUs only if the REGISTER
> request contains "gruu" option tag in Supported header.
> 
> Do you agree or have I missed something ?

This is partially one of those questions like "does a tree that falls 
make any noise if nobody is listening?"

If in fact nobody will learn about this gruu then there is no need to 
create it. But that is all about the difference between the conceptual 
model and the implementation, so it doesn't need to be stated.

The problem arises when there are multiple observers of registration 
state. There are at least two ways this can happen:
- other UAs that register
- subscribers to the reg event package

After you register, if others register they will get your contact back 
in the response to their register request, along with their own. If they 
support gruu, then they will will see the permanent gruu and latest temp 
gruu for your contact.

Similarly, when you register, any subscribers to the reg event package 
will get a notify telling of the change in registration state, including 
your contact and the gruus that were "assigned" to you.

Everything hangs together better this way. Still, if nobody is looking 
you don't have to assign these, as long as you do assign them when 
somebody does start looking.

	Paul

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