On 4/13/16 8:54 PM, Peter Beckman wrote:
On Wed, 13 Apr 2016, Jay Hennigan wrote:
When either of those people dial 9-1-1, where does the ambulance show up?
I suspect your response was sarcastic, but when you dig into what really
happens, it's not nearly as sophisticated as one might hope.
If the numbers are land or VoIP lines, and the address associated with
the
numbers are registered with the Automatic Location Information (ALI)
database run by ILECs or 3rd parties to fetch the address keyed on the
calling number, and the 911 PSAP is E911 capable, they operator will see
the ALI address.
If they're land lines, the NPA/NXX will be local to the CO so you won't
have out-of-area numbers other than a rare corner case of a very
expensive foreign exchange line. If they're VoIP lines, the address is
*supposed* to be so registered, but softphones and even VoIP handsets
tend to move around without the user considering 9-1-1.
VoIP was the scenario to which I was referring. A VoIP phone native to
408-land that moves with a remote office worker to Boston without a
conscious effort on his company and VoIP provider to track it down and
update ALI will reach a PSAP in San Jose or thereabouts. The PSAPs have
forwarding capability but generally only to neighboring PSAPs with a
single button. How quickly will they be able to get the call routed to
Boston, if at all? And as we saw at the beginning of the thread, forget
geo-IP. The ambulance goes to the Vogelmans' farm. If a remote office
worker, it could be VPN back to the VoIP PBX in 408-land anyway.
So, it isn't just IP addresses that aren't easily geo-referenced. It's
also phone numbers. The number may start as a well-referenced PRI going
to an IP-PBX after which all bets are off. If the ANI is the company's
HQ main number where the PRI and IP-PBX are located, then it's just
about impossible to route 9-1-1 from a worker's IP phone in Boston to
the right PSAP.
If they are mobile devices, it depends. Basic gives you nothing (all
phones
since 2003 should have GPS, but people hang on to phones a long time..);
Mobile is a separate case where it's expected that the NPA-NXX isn't
going to be tied to a location. In California, mobile 9-1-1 goes to the
CHP and not the local PSAP based on the cell tower or GPS for that
reason. If not a traffic incident, they forward to the appropriate PSAP
based on the caller's info or perhaps whatever ALI (or estimate) they
get from the cellular provider.
--
Jay Hennigan - CCIE #7880 - Network Engineering - [email protected]
Impulse Internet Service - http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV
