Re: Outbound and mid-dialog requests with GRUU

Dean Willis <[email protected]>
Newsgroups gmane.ietf.sip
Message-ID <[email protected]>
On Oct 17, 2008, at 7:50 PM, Paul Kyzivat wrote:
>>>
>> Not helpful; section 7 refers to out-of-dialog request forwarding.
>
> Why do you say that. That section of outbound doesn't even mention  
> dialogs.
>

It also doesn't mention multiple contacts per GRUU.

>> What happens to in-dialog requests?
>
>> The request references a gruu.
>> A pre-outbound gruu is bound to one and only one contact, so the  
>> request-URI transformation rule is obvious; transform the request- 
>> URI using the contact associated with the gruu. This behavior is  
>> specified in 6.1 of the gruu draft. Oddly enough, that text in  
>> gruu-6.1 replaces the request-URI with "the registered  
>> contacts" (note the plural). Not sure that makes sense. Somebody  
>> tell me if that's a bug in gruu.
>> An outbound-compliant gruu is bound to one and only instance, but  
>> an instance can have multiple contacts.
>> I think what has to happen to make it work is fairly obvious, but  
>> it isn't documented anywhere I can find.
>> There's some hinting at it in outbound-5.3.2, but inly from the  
>> perspective of the edge proxy. What has to happen at the home proxy  
>> to make this work?
>
> I assume the same thing as for out of dialog requests. Out of dialog  
> requests that reference a gruu need just as much to get to the  
> proper instance as in-dialog requests do.

Not really; for out-of-dialog requests, any contact is equally valid.  
But for in-dialog requests, I think there's a need to use the flow  
that was used by the earlier requests in the dialog, if that's possible.

>
>
> Why does it matter if both flows are functional? Presumably if one  
> of the flows has had problems the proxy ought to choose the other  
> one first.

Are there any SIP devices that get confused when they see an  
unexpected request URI on a request, for example, when the request URI  
spontaneously changes mid-dialog without a reINVITE?

Are there other elements that might get confused by NOT seeing some  
messages in a dialog?

For example: what happens if there is an off-the-shelf SBC squatting  
on each flow?

--
Dean

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