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Re: Clocking Sources (was NTp sources that work in a datacenter (was Re: Is latency equivalentto RTT?))
From: "N. Richard Solis" <nrsolis () aol net>
Date: Mon, 2 Jun 2003 16:36:42 -0400


 
 
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


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