[Asterisk-Users] 911 emergency service and VoIP

[John Fraizer]

Joe Baptista wrote:

> I understand that most VoIP providers allow for 911 calling but that 911
> service is not the same as that available to PSTN.
> 
>>From what I understand a 911 Call Will Go To A General Access Line at the
> Public Safety Answering Point (PSAP). This is different from the 911
> Emergency Response Center where traditional 911 calls go.
> 
> Does anyone know how I can get information on howto contact the people at
> the Public Safety Answering Points (PSAPs)?  Is there alist somewhere I
> can reference.
> 
> thanks
> joe baptista
> 

Joe,

You are slightly confused.  Let me explain how it works.

When you place a 911 call, it is sent to the 911 selective router at the 
[I/C]LEC.  The 911 selective router does an ALI (Automatic Location 
Identification) dip against the ANI (Automatic Number Identification) 
that is present on the call.  The ANI is going to be the CallerID number 
that you/your provider present.  When the ALI information is returned to 
the 911 selective router, it makes the decision which PSAP to send your 
call to based on the location in the ALI.  The call is then routed to 
the PSAP.  The PSAP gets the call and the ANI.  They in turn do an ALI 
dig against the ANI to get the location information on their screens.

If no ALI is present in the database for the ANI you're using, the call 
is "default routed" to the county PSAP because no "positive route" can 
be established without ALI information.

When you call 911 without ALI information present, it is "911" service. 
  When you make a call from an ANI that has accurate ALI information, 
you are using E911 or "Enhanced 911" service.

If you have PRI service into your * server, it is possible - though not 
always easy - to set the ALI database information specific for each ANI 
(DID number) that you use.  I do this with our PRI's.  Depending on 
which number we present to the telco, the ALI is different.

Now, what you describe might very well be how Vonage and other providers 
are providing 911 access but, it is most definately NOT even basic 911 
as it doesn't go to the PSAP, even the default-route PSAP.  It is simply 
them mapping 911 calls to go to "NPA-NXX-NXXX" instead.

John