[time-nuts] NIST time services

Chris Albertson albertson.chris at gmail.com
Sat Mar 22 18:55:30 EDT 2014

On Sat, Mar 22, 2014 at 2:25 PM, Brian Lloyd <brian at lloyd.com> wrote:

> NTP running in broadcast mode over a local Gig-E network shouldn't be too
> bad. I suspect timing jitter is pretty low.

Gigabit Ethernet can be actually worse than 100BaseT because of the
way the hardware works.  The packets arrive so fast that interrupts
occurs per several packets, not per packet.  So on Gigabit systems the
NTP packet might not get timestamped correctly because the interrupt
applies to a group of packets that all came in close in time to each
other.  You are best off using 100BaseT

But as I wrote before if you are on a local network and are willing to
buy special PTP compatible hardware you can use PTP and avoid NTP.
PTP relies on external time stamps put on but the network hardware and
is about one order of magnitude better then NTP if you have the right
network hardware.

And if you REALLY care about timing you will distribute a PPS or a
10MHz reference

NTP is best used over the Internet. It was designed for unreliable data links.

Chris Albertson
Redondo Beach, California

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