[ntp:questions] Confused about pool rotation
"terje.mathisen at tmsw.no" at ntp.org
Thu Feb 7 07:17:01 UTC 2013
E-Mail Sent to this address will be added to the BlackLists wrote:
> Cell towers are already synchronized with stratum one
> servers and / or GPS, and usually contain stable oscillators
> e.g. rubidium, cesium, ...
Most (GSM/3G/4G) cell towers make do with OCXOs/TCXOs, but very good
ones, rated at a few ppb/day in drift rate.
I.e. pretty much perfect compared to what NTP usually has to work with.
> Cell towers can't do seamless handoffs for moving cell phones
> to adjacent towers without close synchronization.
The interesting part here is that the actual requirement is for
_frequency_ synchronization, not absolute time sync!
Better FLL corresponds directly with better hand-off performance at
speed: Driving at highways speeds require something like 50 ppb afair (I
was the chief architect for a national cell phone network for a couple
of years), a bullet train requires 20 ppb in order to handle the Doppler
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"
More information about the questions