[ntp:questions] What is the "best" synchronization possible over the network?
Richard B. Gilbert
rgilbert88 at comcast.net
Thu Feb 12 22:21:40 UTC 2009
Hal Murray wrote:
> In article <49920E17.6050007 at tla.org>,
> ntp at tla.org (John Ioannidis) writes:
>> The problem setup: two locations, both within the United States, neither
>> has roof access so no GPS reception is possible. How do you synchronize
>> them with better than 50-microsecond accuracy? Straight NTP over the
>> Internet doesn't do the trick. They don't need to actually be
>> synchronized to "real" time, they only need to be synchronized to each
>> other. Assume reasonably unlimited resources (running a private fiber
>> plant across the continent *is* unreasonable).
>> I've looked into slaving something off a voice-carrier time base, but
>> that's not accurate enough. Maybe something over raw SONET would do the
> SONET gets you frequency, not time. The tick marks (frames) are not
> synchronized across various SONET links. Even the frequency isn't
> locked if the two ends come from different phone companies.
> I think you have several basic approaches.
> If cell phones work where you need the time, that may be an alternate
> to GPS. I don't know what flavor of cell service they use.
A CDMA cell phone base station broadcasts a "reference signal" that
supplies the time. You cam buy a receiver for this signal which will
supply you with time derived from GPS.
Google for CDMA time server.
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