[time-nuts] GPS Outage..

[Magnus Danielson]

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 <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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