Hi Jim,
For Call Data Records (CDR) there isn't no need for significantly better
precision, and for most logging use not either, but for the air
interface, timing has shifted from relatively unimportant to very important.
The trouble is that it is so highly dependent on technology, that
generic statements about cell/mobile technology cannot be made. Time is
also another aspect, and geography. It used to be that the north america
ran its own race on mobile standards (AMPS/DAMPS/CDMA). The nordic
countries ran theirs (NMT), and that converted into the european (GSM)
and then in the next round the world (UMTS). Some technology got
inherited into the UMTS from CDMA. Much got inherited from the
NMT/GSM/UMTS/LTE route. There is also technologies such as DECT and
TETRA and then some national variants of the international ones.
Cheers,
Magnus
On 02/27/2016 11:09 PM, jimlux wrote:
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 <[email protected]>
Date: 2/27/2016 10:54 AM (GMT-08:00)
To: [email protected]
Cc: [email protected]
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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