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

[Peter Lothberg <roll () stupi se>]

> 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)