Re: [sipcore] location-conveyance-03 just submitted

["James M. Polk" <[e-mail]>]

At 02:08 AM 7/14/2010, Thomson, Martin wrote:
> > >The use case is basically: route based on the
> > >value, but provide a reference so that a PSAP
> > >can get better location information later; that
> > >is, updated or more accurate location.  That's
> > >not possible if the UAC does the dereference:
> > >the location information becomes fixed.
> >
> > "...UAC does the dereference"? Do you mean to
> > understand that the UAC inserts location towards
> > an intermediary, gets a rejection 424, with the
> > intermediary's version of where the UAC is -
> > possibly as a location URI, and has to
> > dereference that URI to compose the now dual location MIME body?
>
>No - I'm saying that my major issue is driven by that use 
>case.  There is (currently) no way for any entity (UAC or 
>intermediary) to insert both location by value and location by 
>reference.  There is a need for that capability.
>
> > We mean to have the intermediary do the
> > dereference (if one is needed) and compose in the
> > SIP 424 response a MIME body with both the
> > server's version or both locations of the Target,
> > and for that dual location single presence
> > document to be copied into the next SIP request
> > from that UAC (towards that same intermediary).
>
>Elegant as it is, this just doesn't work.  The UAS (PSAP, LR, 
>etc...) needs to be the entity that does the dereference.  They need 
>to do this because they know how (and when) to make this request so 
>that they get the information they need.  If the intermediary does 
>the dereference, then location information is set in stone from that 
>point onward.

specifically to this last part, if the intermediary does the 
composition - it in fact does know how to do this, but does not do it 
exactly when you may want, and you're right, this is then "in stone" 
without a subscription back to the UAC (geo-filters style) for any 
updates it needs.  I'm not sure you're gonna be able to get away from 
this whenever a PSAP gets a value BTW. It can never be 100% certain 
your getting a reachable location URI for that Target, and the PSAP 
is in the best position to do this "get/update" function.

James