> 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)