[time-nuts] GPS Outage..

jimlux jimlux at earthlink.net
Sat Feb 27 17:09:47 EST 2016


I was thinking about the dispatch center.  When I worked on software for the LAPD ECCCS system in the 80s, timing was established by the OS timing (rsx-11m)  external sync was by wristwatch. 
I doubt it's any more precise now.   They would get a feed from the E911 system.  So the tight timing to get caller location would be in that system, not the PD's system.
The dispatch system needed millisecond response time ( for radio voice switching) but not absolute timing. It ran with a hot standby for fail over and used dual port disk drives. The file system (my part) used OS timestamps.  

Sent via the Samsung Galaxy S®6 active, an AT&T 4G LTE smartphone-------- Original message --------From: Magnus Danielson <magnus at rubidium.dyndns.org> Date: 2/27/2016  10:54 AM  (GMT-08:00) To: time-nuts at febo.com Cc: magnus at rubidium.se Subject: Re: [time-nuts] GPS Outage.. 
Hi Jim,

On 02/27/2016 06:14 PM, jimlux wrote:
> On 2/26/16 11:34 PM, Hal Murray wrote:
>>>> How many of them came from E-911 stations?
>>> E-911 triangulation done on cell towers …
>>
>> I was thinking of the stations where they have the dispatchers who
>> answer the
>> calls
>> and pass the info on to the right people.  I think they need good
>> timing on
>> the recordings, but don't know any details.  I've always thought some
>> of them
>> used GPS.
>>
>
>
> They need good time, but probably only to the nearest second.

Phase alignment is relevant for TDMA based systems as well as CDMA based 
systems, but for a bit different reasons.

GSM for instance actually have phase requirements, but dodges it by 
using one of many options to compensate the phase difference between 
different towers.

Cheers,
Magnus
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