Re: [Sip] GRUU and Mid-Dialog Requests

[Paul Kyzivat <pkyzivat at cisco.com>]

Xavier Marjou wrote:
> > subsequent (in-dialog) requests are already sent to a specific UA
> > instance by virtue of the Contact header and the Record-Route for the
> > dialog. 
>
> I agree that in-dialog requests are already "sent to a specific UA by 
> virtue of Contact". However, my understanding is that Record-Route headers 
> are "only" required for the GRUU draft because GRUU are advertised in the 
> Contact header fields, and not because of a use-case related requirement.
>
> > The point of GRUU is to allow out-of-dialog requests to target a
> > "specific instance" in the same way that in-dialog requests do. 
> > No more, no less.
>
> The point is that additional processing is needed by the current draft in 
> home proxies. To remove this (not-needed?) burden, one could imagine other 
> ways to advertise the GRUU (e.g. a Contact-Gruu header field) instead of 
> advertising it in the Contact header field (e.g. in a 200 of INVITE). The 
> remote user-agent would use this other way for initial requests (e.g. if it 
> wants to send a SUBSCRIBE), without impacting the routing of mid-dialog 
> requests in home proxies.

What you (I think) are suggesting was considered long ago. But it was 
discarded for a variety of reasons. Jonathan can probably dredge them 
out of his memory better than I can.

In any case, no matter how it is done, when a UA doesn't have an address 
of its own with the gruu property, then it will need to get one from 
some server elsewhere. That server will then have to take action every 
time that gruu is used. At best you could avoid a small amount of work 
on in-dialog requests. But chances are the home proxy would still have 
to record-route, because in-dialog requests would have to transit some 
box that has addressability to the UA.

	Paul

> I'm sorry to bring this discussion so late, I just realize this lately.
>
>
> > > Other minor comments:
> > >
> > > p11: in the properties that a GRUU must exhibit, add that the host 
> > > part of the URI must be equal to the host of the registrar that owns
> > > the GRUU.
>
> > I don't agree that is a requirement. It could be a different host 
> > part that maps to the same IP, or a different host part that maps 
> > to a different IP but the same server, or it could map to a 
> > different server with access to the same location server.
>
> Ok, agreed. However, maybe just rephrase my first proposal by indicating 
> that the host part of the GRUU must be under the responsability of the 
> domain that creates the GRUU. 

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