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 <m...@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.kletni...@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. > > > >