Subject: [Ecrit] How to verify that the call is addressed to a PSAP?

From: "Tom-PT Taylor" <[email-masked]>
Date: Wed, 21 Dec 2005 10:37:50 -0500

There is a requirement (too lazy to look up the number) that a call 
routing element (e.g. SIP proxy) handling a call with an emergency 
identifier must ensure that it is directed to a PSAP.  We've refined 
this slightly in the security draft to say that this is necessary only 
if the call routing element would normally authenticate the caller for 
billing or authorization, but doesn't because it's an emergency call.

Anyway, this raises the question: how does such a verification take 
place?  Do we think of this as a different type of query on the mapping 
database: is this destination URI one of the ones you map to?

Tom Taylor

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From: "Brian Rosen" <[email-masked]>
Date: Wed, 21 Dec 2005 11:07:00 -0500

I'm sorry, I can't follow this.

Are you talking about a proxy that IS NOT doing the mapping?
If it is doing mapping, then I don't see any issue; the mapping tells you
where to send the call.

If it's not mapping then we have two cases:
	Before the map
	After the map

Before the map proxies are responsible to forward the call to a proxy that
does the mapping.  That should be clear and simple

The circumstance you seem to be describing is a routing proxy that is
handling a call after it is mapped, before it gets to the PSAP.  This would
include, I guess, an ESRP.  Are you suggesting that it somehow queries the
mapping database to see that this is one of the legal URIs for that kind of
emergency?  That seems pretty pointless.  I think it should route the call
to the Request URI specified, period.

Brian

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Tom-PT Taylor
Sent: Wednesday, December 21, 2005 10:38 AM
To: ECRIT
Subject: [Ecrit] How to verify that the call is addressed to a PSAP?

Tom Taylor

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From: "Tom-PT Taylor" <[email-masked]>
Date: Wed, 21 Dec 2005 11:34:48 -0500

Here's the scenario I'm concerned about:

-- the system assumes that mapping is done in the emergency caller's device

-- the caller hacks his device to mark the call as emergency but send it 
to a destination of his own choosing

-- this gets around the ordinary billing procedures, so the caller gets 
services for free.