GPS attack vector

Lamar Owen lowen at
Thu Jan 17 13:57:20 UTC 2013

On 01/16/2013 08:06 PM, Jay Ashworth wrote:
> Do you use GPS to provide any mission critical services (like time of day)
> in your network?
> Have you already see this? (I hadn't)
Hi, Jay,

Yes, saw this about a month ago.  We have a UNAVCO Plate Boundary 
Observatory station (779) on our site, and it uses a Trimble NetRS.  We 
also use GPS timing locally to generate NTP stratum 1 for our LAN via 
Agilient/HP Z3816 disciplined receivers, and individual GPS receivers 
for both of our 26 meter radio telescopes for precision local standard 
of rest calculations.

But as a frequency standard for 10MHz, we only use the output of the 
frequency locked loops in the Z3816s as references for our Efratom 
rubidium standard; even cesium clocks have more drift than rubidium 
ones, and the rubidium is manually locked, and is the master reference 
for anything that needs a frequency reference; the Z3816's can have 
significant jitter (well, significant is relative.....).  Last I 
checked, the rubidium was 8.5uHz (yes, microHertz) off according to the 
GPS disciplined 10MHz signal from one of the Z3816s (we use an HP 
differential counter with a very long gate time to get that measurement 

It was interesting timing for the release of this paper, as it was 
around the time tick and tock were rebooted and went all 'Doc Brown' on us.

Anyone interested in the vagaries of serious time precision, please 
reference the 'Time-Nuts' mailing list, and other content, hosted by

More information about the NANOG mailing list