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Re: Clocking Sources (was NTp sources that work in a datacenter (was Re: Is latency equivalentto RTT?))
From: Peter Lothberg <roll () stupi se>
Date: Sat, 31 May 2003 23:22:40 PDT


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)


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