[Asterisk-Users] 911, networks of * servers, etc. (was: VOIP Dialtone?)

[John Todd]

OK, that "VOIP dialtone?" thread was getting really out of hand, so 
I'll condense my answers into one big ugly message:


1) 911 service.  Yes, that is one of three reasons to keep your PSTN 
line.  The other two reasons are:   Inbound calls from local callers 
still should work on a POTS line, for now.  You can't find VOIP 
providers in most area codes, so you'll most likely need to have a 
"local" number that finds it's way to you for "local" tasks. 
Secondly, the Internet is not as reliable as the phone system. 
Sorry, folks, it just works that way right now despite what your 
network engineer might tell you.  That's not to say it's unreliable, 
but those last two nines are very expensive... Besides, any good 
network engineer will tell you that you should have multiple paths 
for your IP connectivity.  With few exceptions, most homes do not 
have multipath connectivity.  (note: businesses may in fact have 
better uptime on their IP network than their phone network, if they 
have competent engineers and a reasonable budget.)

1.5) There are reasonable technical solutions to this problem, but 
for the life of me I can't figure out why the 911 centers haven't 
gotten their act together and solved this.  There are two halves to 
this problem: "What PSAP do I call? (and what phone number)"  and 
"How do I get my location data to the PSAP once I call them?" 
C'mon, this is not difficult.  The first question can be answered 
trivially: there _must_ be a database of address-to-PSAP mappings. 
Any PBX administrator (or SIP phone owner, for that matter) should be 
able to figure out their address.  Methods for associating the PSAP 
number with the phone are numerous, and trivially implemented - if 
people don't keep their address information updated, they're SOL 
(though you can remind them in an automated fashion to keep it 
updated - just forbid them from using the service unless they verify 
the address every month or so.)

The second question is more difficult, but certainly possible.  There 
may be kludge ways of doing it, and there should be more elegant ways 
of doing it.  A SIP header with lat/lon/alt data that gets sent from 
the UA only on 911 (or other programmable string) calls might be 
reasonably elegant... maybe.  But that only gets the data to the SIP 
proxy.  That doesn't solve the issue of how you get that data from 
the SIP proxy to the PSAP, which at some point will be almost 
certainly through a PSTN connection... ADSI FSK, maybe?  Ugly, and 
PSAPs would not want to invest in equipment.  A national caller-id to 
location clearinghouse in which your proxy could participate (any 911 
calls would create a temporary mapping)?  Maybe, but probably not. 
Non-standard, and I doubt PSAP operators would want another tool, 
even if it is web-based and so easy a monkey could use it.  I don't 
know.  I guess I'll grill the PSAP people at the panel next month at 
VON.  :-)


2) Networks of Asterisk servers, offering dialtone to each other in 
different places.  YES, this is a good idea, but setting dialplans up 
for least-cost-routing via static routes is a pretty rotten and 
unscaleable task.  See my conversations on why someone should 
implement TRIP in Asterisk (hey, I'm still looking for a 
programmer... anyone want some money?)
   http://lists.digium.com/pipermail/asterisk-dev/2003-July/001172.html

I already participate in one such network, and I get free calls into 
four large area codes into which I terminate much of my traffic, and 
they get... well... not much, since I live in an area code that gets 
very little traffic.  :-)  They get my undying gratitude.


3) Local service vs. long distance:  I route local (read: "free") 
calls over my PSTN connection.  I make very infrequent local calls, 
but it seems to work well for me.  I could, probably without 
noticing, send all my calls through my LD provider, even those which 
are local, and not notice a change in my bills.  The cost for a 
business when you examine the measured service that most businesses 
use vs. the cost of LD, is a silly comparison - it's very often 
cheaper to dial via a VOIP provider than it is to dial a local 
measured RBOC call.   Go, Go, Gadget Deregulation!!  Uh... wait... 
"de"regulation?   This may be illegal if you're a CLEC/LEC, but if 
you're not a phone company, go right ahead.

4) To whoever asked, http://www.voicepulse.com/  should work with 
Asterisk, as they are SIP based.  I don't know if they give you 
username/password though - I didn't look that far into it.

JT