Re: Is REFER within dialog part of INVITE or subscription usage? (was RE: SIP INFO)

Doken, Serhad wrote:

>> I guess the question is: would it be valid to send a REFER within an
>> existing dialog that had no INVITE usage? If it were valid, presumably
> 
> Yes, I think so.
> 
> 
>> it would have the same meaning as sending one outside a dialog, except
>> that the resulting subscription would share the dialog. I expect that
>> is
>> a usage it would be difficult to find in the wild.
> 
> Consider a third party control application that forces an endpoint to register :
> 
> REFER sip:phone.doken.com SIP/2.0
> Refer-To: <sip:[email protected];method=REGISTER>
> 
> that triggers a REG to the registrar as :
> 
> REGISTER sip:[email protected] SIP/2.0

You are suggesting that first this 3pcc application sends a SUBSCRIBE to 
this UA, establishing a dialog. Then it sends a REFER within the dialog, 
asking the UA REGISTER? That then would presumably result in a 
subscription to the refer event package sharing the dialog with the 
prior subscription. I guess this is *possible*, though I don't know 
*why* it would be done. What would the initial SUBSCRIBE be to, and how 
would it be established before the UA has registered?

Are you aware of such usage in the wild?

(Its incidental to this discussion, but REGISTER presents unique 
challenges because of the way addressing works for it. Contrary to your 
example above, we would typically expect that the To: would contain the 
full URI, while the R-URI would only be sip:doken.com. This would 
require more special case processing.)

	Thanks,
	Paul
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