Subject: [Sip] Location Conveyance only of UAC location

From: "Rosen, Brian" <[email-masked]>
Date: Tue, 1 May 2007 13:36:13 -0400

An issue raised by reviewers for location-conveyance was how it works if
the UAS tries to send its location to the UAC.  There are several things
that are problematic with this, including errors: the UAC can't tell the
UAS about an error it finds in the location.

We propose to resolve this by specifying that location-conveyance sends
the location of the UAC.  The header can appear in a message from the
UAS to the UAC, but it means that the UAS is looping back the location
of the UAC.  

The other end can send its location with an UPDATE or ReINVITE, turning
around the connection (i.e. becoming the UAC).

The loopback procedure is useful when proxies insert location.  The UAC
may not even be aware that it happened, and yet it gets an error or a
result it doesn't understand.  If the UAS echo's what it gets, the UAC
can see it.

If this proposal finds favor with the working group, we will modify the
text in the next revision of -conveyance to incorporate it.  

Brian

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From: Paul Kyzivat <[email-masked]>
Date: Tue, 01 May 2007 14:06:43 -0400

> text in the next revision of -conveyance to incorporate it.  

This sounds wise to me.

Something that bears further discussion: is an intermediate node 
permitted to drop the location from a response? I think there are 
competing interests here - some intermediate nodes may want to drop it, 
while the UAC would prefer to have it retained.

	Paul

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From: Richard Barnes <[email-masked]>
Date: Tue, 01 May 2007 21:01:11 -0400

I think this is the correct, unambiguous semantic for the Geolocation 
header.

I'm less certain about how well the loopback will work in practice, for 
the reason Paul noted (you might get push-back on loop-back, haha), but 
as long as it's not a MUST, that's not a big deal.

--Richard

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From: [email-masked]
Date: Wed, 2 May 2007 22:34:00 -0400

From: "Rosen, Brian" <[email-masked]>

Ouch.  That could be quite a problem.

This does seem to be the correct solution.  I suppose you could even
extend this mechanism to include sending an OPTIONS with a
location-conveyance header.

Good point.

   From: Paul Kyzivat <[email-masked]>

It seems best to require the intermediate node to retain the
location-conveyance.  At least, unless there is no error or warning
referring to it.  But assuming that locations aren't added to messages
frivolously, why would intermediate nodes want to drop it?

Dale