[LINK] RFI: Clock Synchronisation in Hosts

Bernard Robertson-Dunn brd at iimetro.com.au
Wed Nov 12 14:14:55 AEDT 2014

On 12-Nov-14 12:21 PM, Roger Clarke wrote:

> What's the impression of Link Institute members about the frequency with which hosts in professionally-run organisations synch with time-servers?

If by "hosts in professionally-run organisations" you mean those with 
data centres, they have their own clock time source (GPS synched or 
atomic clock). This is known as a Stratum level 0. This would be 
connected to an NTP server which provides a Stratum level 1 capability 
for the rest of the data centre. Each time there s an extra hop, the 
level number goes up. Stratum 2, 3 etc.
Synchronisation is done on a sort of continuous basis. I say sort of 
because it's part of a feedback loop. The clock to be synchronised 
checks its internal time against the reference and doesn't just reset to 
correct time, it adjusts itself to run more accurately.

At the Stratum 1-2 levels tolerances are in the tens of millisecond 
ranges. If you need time stamps, that's what you need.

No self respecting data centre would use an external source.

See here for more gory details



Bernard Robertson-Dunn
Sydney Australia
email: brd at iimetro.com.au
web:   www.drbrd.com
web:   www.problemsfirst.com
Blog:  www.problemsfirst.com/blog

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