[Asterisk-Users] 911 settings.

John Todd jtodd at loligo.com
Fri Dec 19 20:26:50 MST 2003

At 5:26 PM -0500 12/19/03, Andrew Thompson wrote:
>  > I would like to know if anyone has come up with a script for 911 dialing
>>  rules that put correct information on our locations.  We have our office
>>  in 3 different building one being our production & shipping dock.  It is
>>  almost 2 blocks away.  We are connected with Ethernet Wireless between
>>  the buildings and have Sip phones setup in the other 2 locations. All
>>  the phones are working just fine.  But when they call 911 they get our
>>  main address and not the other address's.  So we need to be able to give
>>  the correct address to the 911 call!  This is just for our locations and
>>  not for reselling our Asterisk server!
>The 911 office is most likely retreiving the address off of the line that is
>placing the call. Do you have any voice lines in the other buildings?
>I would consider a line siege device and FXO attached to a fax or security
>system line in the other buildings. Route the dialed 911's out over the
>local pots line and they will get the correct address. I don't know if you
>can attach an address any other way.
>You could try sending a different callerid, but if they are all billed as
>being in the main building, that's probably the address they'll get.

Aye, there's the rub.

I'll be brief on 911 and VoIP, but it's a topic about which I could 
complain several days.  The problem is threefold:

   1) which 911 center do we connect this VoIP user to?
   2) what caller ID do we give to the 911 center?
   3) how do we get street address to the 911 center for dispatch?

Some providers Whose Names Will Go Unmentioned Here have come up with 
a system that they are selling to large VoIP service 
providers/IPSCP's.  Without violating any NDA's (see references for 
public information sources) here is the general view for each option:

1) If you have the address of the customer, this E911 provider allows 
you to send (via XML over HTTP, apparently) the address information 
of the customer and their phone number to the central database.  The 
central database then feeds back to you the ten-digit phone number 
that lets you into the "normal" phone line for the 911 center.  It's 
then your job, as the IPCSP or PBX provider, to send the call the 
correct path to get to that ten-digit number.

2) Good question, especially with VoIP phones.  No "true" solution 
exists for this across all providers; it depends on implementation. 
If you have DID's associated with each station, you're in luck.  If 
you are using twelve digit random extensions, all homing out of one 
single DID for outbound caller ID, then you'll have to come up with 
some clever way around that, won't you?  My favorite is a temporary 
mapping of some small pool of DID's to the last SIP URI's that made 
911 calls - you have maybe a block of 1000 numbers that you 
round-robin and attach to 911 calls so that when the PSAP calls back 
the DID, they get auto-mapped to the SIP URI of the original caller. 
Maybe two or three days later, that number gets re-mapped somewhere 
else...  I haven't discussed this idea with any PSAP operators, but 
I'd be interested in opinions from the list as to it's usefulness.

3) You send your customer list and address information via some type 
of update to a central repository.  That repository is hooked into 
the brains of some of the 911 systems across the country (but 
potentially not all of them.)   The database is called ALI, or 
Automatic Location Information.   Updating ALI unless you are a large 
phone company (or ALI service provider) is very difficult, and is 
normally a very expensive proposition.  Small or medium PBX systems 
like Asterisk will be left far, far behind in this because the users 
are typically low-budget and don't have the time to waste building 
"relationships" with fussy sales- or paperwork-heavy organizations 
which can provide those services.  In any case, not always is it the 
case that the ALI provider can push the street address information 
all the way out to the PSAP, and also there is often a logical 
disconnect between the ALI data and the phone call itself if you're 
in a VoIP environment.
   Keeping the addresses updated in the ALI is 100% the problem of the 
ITCSP - there are at least four methods of this that have been 
discussed previously to solve this at a policy and technology level, 
all with various faults and favors, a combination of which I'm sure 
could see "acceptable" accuracy given the technology gap.
  Yes, it's much more complex than this, but I said I would be brief...

Solution: What is needed is a VOIP-CLUEFUL provider of E911 PSAP 
mapping data, ALI transfer, and maybe even SIP call forwarding and 
processing to PSAPs.  They should be low-priced on a monthly basis 
($1 a line?), have IP connectivity to customers across the public 
Internet, be open-source for their client-side implementations, and 
provide (possibly) reverse call mapping for customers via DIDs.   I 
would even support the construction of a non-profit company sponsored 
by NENA or <shudder> the gub'mint if this could be made into 
something that would benefit the Public.



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