On the other hand, maybe all you want to do is to route the
call to the right E911 center. In that case, as long as you
are in the right county you are probably OK.
If all you use the "last known position" information for is routing to the correct E911 system, that might be okay. However, one thing I believe you need to also transmit along with the position information is "time since last fix", so that you can get some sort of idea how long it's been since that position information was reasonably accurate.
If the time since last fix is several hours, then the person might now be on a plane using a picocell or broadband wireless network connection that is not position-enhanced, and using the position information for routing to the presumed correct E911 system may be inappropriate.
So long as we give additional information which gives the system an idea of the expected level of age and error in the information, I think the risks should be able to be reasonably minimized.
In any case, no solution to E911 and VoIP is likely to meet
100% of its requirements, but if you can improve the situation
significantly, then it is still worth doing.
I guess it also depends on what you mean by "significantly". Is a 10% solution significant? Do you need 90% before you're significant? And what's the cost of false positives, as well as false negatives? I think all these factors need to be considered, when looking at potential solutions.
I guess it also depends on what you mean by "significantly". Is
a 10% solution significant?
Nope. 15% or better.
This comes from an old rule of thumb about sales, pricing, etc.
If the new supplier doesn't offer 15% or better pricing then
the hassles of switching aren't worth it. Or, you can increment
the price and keep the business as long as you don't go higher
that 15%.
Of course in big business, you are more likely to study the
actual costs and implications to find an optimal solution.
Somehow I suspect that the current FCC regulatory environment
is not one in which such detailed studies will be done before
deciding. So it's back to rules of thumb and letting the market
hash out the details by making mistakes.
--Michael Dillon
If a person is calling 911 from a plane in flight, are
we really so concerned about which PSAP receieves the
call? The last known fix would likely have been the
point of origin in any case...
David Barak
Need Geek Rock? Try The Franchise:
http://www.listentothefranchise.com
If a person is calling 911 from a plane in flight, are
we really so concerned about which PSAP receieves the
call? The last known fix would likely have been the
point of origin in any case...
If a picocell on board an airplane receives an E911
call, it shouldn't route it to any PSAP. The first
responders in this situation are the flight attendants
so it should ring the flight attendant's phone.
By the way, if GPS works in the air for small aircraft
pilots, then why wouldn't it work for cellphones? The
last known fix should be 100% up to date and 100% useless.
--Michael Dillon
GPS does not work through the fuselage of a aluminum airplane.
I've tried. More than once.
GPS does not work through the fuselage of a aluminum airplane.
I've tried. More than once.
The gps carrier frequency is 1575.42mhz
a decent gps antenna is unfortunately a bit larger than most small gps recivers let alone cellphones. multipath cancelation is a serious issue when dealing with gps, and being in a aluminum tube mailer, under tree cover or inside commercial construction doesn't help your situation when all you have is a tiny patch antenna printed on a pcb.