NIST NTP servers

Wed May 11 19:10:57 UTC 2016

No, many cell carriers run their own completely independent timing networks. I support some head-ends where they have rubidium clocks and a T1-delivered time source. They do reference GPS, and many cell sites have GPS as a backup clock (you can see their conical antennas on the very top of the tower). But most cellular providers are very protective of their time sources. They’re also typically clocking SONET networks too, which requires BITS.

 -mel

JAshworth said:
> CDMA and GSM are false diversity: both network types nodes *get their time* 
> from GPS, so far as I know.

> On May 11, 2016, at 10:54 AM, Valdis.Kletnieks at vt.edu wrote:
> 
> On Wed, 11 May 2016 15:36:34 -0000, "Jay R. Ashworth" said:
> 
>> CDMA and GSM are false diversity: both network types nodes *get their time*
>> from GPS, so far as I know.
> 
> I'll make the fairly reasonable assumption that most readers of this list have
> networks that span multiple buildings.
> 
> If somebody is managing to figure out that you have a GPS in Building 37, and a
> GPS-based CDMA up on the corner of Building 3, and the *other* 4 clocks at
> other locations and getting close enough to all of them at the same time to
> conduct a successful spoofing attack, all just to move your time source a
> few seconds off....
> 
> ...  then the fact that GPS is spoofable is probably *NOT* your biggest
> security problem.
> 