Re: Vonage Selects TCS For VoIP E911 Service

[Brad Knowles <brad () stop mail-abuse org>]

At 6:45 PM +0200 2005-07-19, Mikael Abrahamsson wrote:

>  I think the ground based radio transmitters needed for indoor operation
>  isn't around much outside the US. I was very surprised when I got a
>  cellphone-based GPS navigator from AVIS last time I was in the US, and
>  it started working inside the terminal building.

	I had one of those, too.  It was a Nextel phone.  However, I 
don't believe those use actual GPS signals.  I believe those are 
actually using triangulation from the cell phone towers (e.g., Time 
Difference of Arrival, Angle of Arrival, and/or Enhanced Observed 
Time Difference).  They aren't as accurate as GPS, but they will give 
you reasonably accurate position information anywhere you can get a 
decent cell phone signal.

	I have heard about new highly accurate/low-cost single-chip 
clocks that would help improve accuracy of cell phone tower 
triangulation, and would hopefully also be something that could be 
put in standard desktop and laptop computers, making it much easier 
to run software such as NTP to keep the system clocks much closer to 
the correct time.

--
Brad Knowles, <brad () stop mail-abuse org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

    -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
    Assembly to the Governor, November 11, 1755

  SAGE member since 1995.  See <http://www.sage.org/> for more info.