[ntp:questions] Confused about pool rotation

Terje Mathisen "terje.mathisen at tmsw.no" at ntp.org
Thu Feb 7 15:18:32 UTC 2013

Mike S wrote:
> On 2/7/2013 2:17 AM, Terje Mathisen wrote:
>> Most (GSM/3G/4G) cell towers make do with OCXOs/TCXOs, but very good
>> ones, rated at a few ppb/day in drift rate.
>   ...
>> The interesting part here is that the actual requirement is for
>> _frequency_ synchronization, not absolute time sync!
> You're probably not familiar with CDMA systems, which absolutely MUST be
> synchronized in both time and frequency.

I'm quite familiar with CDMA, I have used Endrun's CDMA reference clock 
on a server in Tampa, FL.

I wrote GSM above specifically to avoid having to go into these issues, 
besides taken world-wide CDMA is much less common.
> http://www.cdg.org/technology/cdma_technology/a_ross/systemtime.asp
> Hence the appearance of surplus GPSDOs, like the HP Z3801A, which was
> part of a Nortel CDMA BTS.

That is very nice side-effect, yes!


- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

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