phone fun, was GeoIP database issues and the real world consequences

Jay Hennigan jay at
Thu Apr 14 05:22:46 UTC 2016

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 - jay at
Impulse Internet Service  -
Your local telephone and internet company - 805 884-6323 - WB6RDV

More information about the NANOG mailing list