Generally speaking, the implementation of time and frequency synchronization networks is divided into several stages including installation of various time/frequency synchronous equipment such as time/clock source, transmission/bearer devices and wireless base station, service commissioning and opening, performance validation and acceptance of the networks, service cutover and network maintenance & management. Here we draw an overall test flow of engineering maintenance when implementing such networks, as shown in Fig 1.
Fig 1 Test Flow of Engineering Maintenance in Time/Frequency Synchronization Networks
For different stages during the implementations, the test items, methods and focus about the devices of the networks are quite different. Here are the explanations.
Installation stage: the symmetry issue of the fiber is the main point. Generally a pair of fibers in same cable and patch cords of same length are used to reduce the connecting asymmetry effect to the measurement
Joint-Debugging stage: the main points are in time and clock settings, interoperability of various equipment, asymmetry compensation, asymmetry compensation of protection paths, time error and clock frequency offset test
Check and Acceptance stage: the main points are time error, clock frequency offset, long-term time error and frequency offset, clock wander, effect on time and frequency synchronization when switching the lines, switching and holdover of time servers
Cutover stage: the main points are monitoring of key nodes like time/frequency monitoring at furthest base stations, and to check if the services has impact on time and clock system
Maintenance stage: the main points are routine and regular spot test, long-term test on key nodes, troubleshooting, etc
