What are the specifications for the holdover synchronization mode in the Cisco ONS 15454?
A. A receiver clock enters holdover mode when it loses all its timing references for a significant period. The main contributors to holdover performance are: • Initial frequency offset • Frequency drift • Fractional frequency offset due to temperature variations According to GR-253 recommendation, the values must be better than these: • Initial frequency offset less than 0.05 ppm • Frequency drift less than 5.8 x 10 (exp -6) ppm per second • Fractional frequency offset due to temperature variations less than 4.1 ppm The summary of those three must be less than 4.6 ppm per day in first 24 hours of holdover mode. Technical specification for the Cisco ONS 15454 is even better than requested in the GR-253 recommendation, as shown here: • Holdover stability, including temperature variation frequency offset, is 3.7 ppm per day. • It results in less then 255 slips in first 24 hours of holdover mode.
