Experiences with 911 calls and SIP

Hi all,

I'm having a discussion with one of my vendors about the 911
capabilities of their SIP VoIP phone system. The vendor says that if we
use an Enhanced 911 service that their phone system will transmit
location information to the PSAP at the time of the call in addition to
the ANI. I was under the impression that this functionality was not
possible, hence all the problems that Vonage is having. Can anyone help
clarify this for me?


Are you buying just the hardware or the service as well?

If you are buying some voice-related service, there's absolutely no reason
why they *can't* be transmitting ALI/PS (that's location identification)
along with the ANI when 911 call is placed.

The reason Vonage didn't do it is because they a) didn't want to do it b)
didn't have to do it. Both have now changed and Vonage is busily working
on e911 integration.


The vendor *CAN*, if they are properly connected to the selective routers
and ANI/ALI database, both route the call to the correct PSAP and display
the location of where you *TELL* them the phone is located.

He isn't technically correct that the system transmits location information
to the PSAP at the time of the call. The system transmits ANI (calling
number) and the PSAP queries a regional database to obtain the location.
It can take several hour sor even days to update the database if you move.

In most cases, telephone service providers *MUST* maintain a toll-free
number available to the PSAP operators 24/7. In the event of missing or
incorrect location information, the PSAP can call the carrier who *MUST*
answer with a human being[1], not an auto-attendant. That person can
then tell the PSAP the current location of record.

If you take your Xten laptop to Bangladesh and register your SIP phone
there, don't expect the ambulance to arrive where you *ARE*, only where
you told your carrier the phone was located.

The same issue occurs with off-premise stations to analog PBX systems
and the like. G.I.G.O.

[1] I suppose that the human being could be in India and give the same
level of service we've all grown to cherish from SBC and AT&T...

Given the state of flux that VoIP is in right now regarding E911, your
best bet may be to set up the PBX at each site to route 911 to a bank of
two or three outgoing POTS lines.

(I will be very interested to find out what you eventually decide. In
addition to the work I'm doing at JustThe.net, I'm working at another
California school district, and our assistant IT director is talking about
possibly going VOIP in the next few years.)

I can't see any reason it wouldn't be possible with appropriate cooperation
from the Telco and Government agencies involved. However, the real question
is how do they know the location and which PSAP to route you to. Your
SIP phone could be anywhere in the world, literally, without changing
about it's SIP registration other than the IP address (and, with VPNs, maybe
not even that).