Cellular carriers also use GPS timing for many reasons that are not readily apparent at the layer 3 router/IP/BGP network level. One big need is RF related, back-to-back sector antenna frequency re-use with GPS synced timing on the remote radio heads, such as an ABAB configuration on a tower or rooftop site. The same with some much less costly near consumer grade WISP radio platforms and PTP radio systems nowadays. In such a configuration the GPS timing signal from the local GPS receiver (small cone shaped or puck antennas at the site) is actually the primary, and whatever NTP-based GPS signal the network node might have access to is secondary. On Wed, May 11, 2016 at 12:10 PM, Mel Beckman <mel@beckman.org> wrote:
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@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.