Mark R. Lindsey writes:

 > So, in numerous cases, there is a SIP box between the SIP phone and  
 > the Service Provider. In many networks, including those with WiFi  
 > phones, the UAC can be compelled to register only through that B2BUA.

even if they register through their enterprise boxes, the UAs can still
be located wherever else than at that office.  people use vpns to get to
their offices from home/road/etc.  so i would say that it is actually
more harmful to give wrong location info (that of the office) than not to
give anything at all.

 > This is both a location-sensing & policy enforcement problem:
 > 
 > (a) If the location can be sensed by the enterprise operating a proxy/ 
 > B2BUA, then a proxy between the UA and the PSAP can insert the
 > location.

it is very hard to sense at the enterprise where my wlan hotspot
attached phone really is.

 > (b) If the location can be sensed by the UA, then it can insert its  
 > own location.

mobile networks do have location info, but they don't want to give it
out to the ua.  so if your sip service is not provided by your mobile
operator, you get nothing.   this actually proves that authorities value
much more business rights of mobile operators than safety of people.

 > (c) Else, if no location is provided to the service provider, an SP  
 > responsible for properly delivering emergency calls would refuse to  
 > let a device register.

if you make such a law, sure there will be location info given, but in
many cases it will be bogus and thus more harmful than no info at all.

but this is not really a sip wg discussion other than it has been made
to spend its cycles on yet another useless standard.

-- juha
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