Wireless Home Networking - Index of

The 911 emergency services used in standard
landline (POTS) phone systems are well-honed,
well-oiled machines that have been developed
over decades and decades. POTS phone systems
have extensive directory records in place
that know exactly where each phone is located
(the name of the subscriber, the address, and so
on). So when you make a 911 call, emergency
officials pretty much know instantaneously
where you are calling from and can react
accordingly.
Mobile (cell) phone systems now have similar
capabilities, due to the adoption of a technology
called Enhanced 911 (or E911). Mobile phone
operators use either a specialized radio triangulation
technology in their networks (which
determines where you are based on how long it
takes your signal to reach several cell towers in
your area) or a GPS chip embedded in your cell
phone to determine your location and pass it on
to authorities in case of emergency.
VoIP and 911, however, have a more tenuous
relationship. The nature of VoIP gear (even
wired VoIP gear) means that it can be plugged
into a broadband connection anywhere — so
there’s no one-to-one relationship between
your VoIP phone number and your current location.
Your IP address doesn’t provide the kind of
location information that a traditional phone line
does — in fact, your IP address could frequently
change as your ISP rotates IP addresses among
its customers.
It’s hard for a VoIP 911 system not only to tell
authorities where you are, but also to route your
Chapter 13: Using Your Wireless Network for Phone Calls
VoIP and 911
911 call to the right 911 call center. If, for example,
you take your VoIP phone to work, you might
be in the coverage area of an entirely different
911 call center than you are at home — currently
there’s no way for VoIP systems to know this.
So VoIP providers are required to give you more
than ample notice that they are not as good at
handling 911 calls as are landline or even mobile
phones. Some providers give you the opportunity
to register your VoIP phone equipment with
your current address information — this can
then be used to route your 911 call and to provide
the 911 folks with your address. If you’re
using a VoIP system as your primary home
phone system, we think you should absolutely
take this step and register for your VoIP
provider’s 911 system. (If they had bothered
asking us, we would have simply told them to
put GPS chips into all VoIP phones and the problem
would have been solved!)
One last fact to keep in mind about VoIP and 911
and other emergency calls: Unlike POTS phones
(which get their power from the telephone line
itself), VoIP phone systems need external AC
power to work. If your power goes out, it’s likely
that both your broadband connection and your
VoIP phone or telephone adapter will also go
out. If you move entirely to VoIP in your home,
we recommend that you purchase an uninterruptible
power supply (UPS) and make sure that
your broadband modem, wireless router, and
telephone adapter are all connected to it. This
won’t keep you up and running for days at a
time, but it can keep the phones working during
brief power outages.
245