Clocking Sources (was NTp sources that work in a datacenter (was Re: Is latency equivalentto RTT?))

Mon Jun 2 20:36:42 UTC 2003

Peter Lothberg wrote:

>
> > The desire for everyone to have a timing source that is tracable to
> > a Cesium clock comes from the SONET standard.  If you tie two SONET
> > networks together, if they both don't have timing that's tracable to
> > a Stratum 1 (PRS) source, they'll drift at the points where they
> > interconnect and PSE (Positive Stuff Event) and NSE (Negative Stuff
> > Event) errors will be the result.  This is BAD BAD BAD for the voice
> > networks that are provisioned over SONET.
>
> BITS and SONET systems do not carry time-of-day information. It's only
> frequency.
>
> Sonet/GR253C SDH/G811 stratum-1 is 1x10-11 that will give you one
> pointer update every 72 days. But you can do one pointer-update every
> two frames...
>
> -P
>
> (you do stuffing on PDH systems)
>

I reread my post and I didn't think I mentioned TOD information being a part of the BITS/SONET requirements.

BUT, most if not all BITS systems that have a GPS component will also provide an NTP feed derived from the almanac and TOD information provided by the satellites.  That's true of the Datum and the Symmetricom products and I'm pretty sure of the Larus products as well.

-Richard