During the running of equipment, user adjusted the optical fiber connecting with the eastward and westward optical interface unitof No. 3 NEas required. After the adjustment, the receiving and sending optical powers of No.3 NEwere tested, the result showed they were normal. However, when optical fiber was connected to optical interface unit, SBS NM reported that there were large amounts of TU pointer justifications and bit errors in the tributary paths of No.1, 3 and 4 NEs.
1) It was judged that the clock of No.3 NEor No.4 NEwas asynchronous with that of No.1 NE.
2) The clock configurations of respective NEs were checked, the result showed they were correct.
3) Since the system was in normal operation before optical cable was adjusted, the fault might be caused by optical cable adjustment. For path protection ring, the eastward and westward optical fibers of NEwere connected reversely, in a short term, the services were normal except that its performance would be affected. The connection direction of No.3 and No.4 NEs were checked carefully, it was found that the eastward and westward optical fibers of No.3 NEwere connected reversely.
4) After the optical fibers of No.3 NEwas connected again, it was observed that the pointer justifications and bit errors of the system all disappeared.
After the reason was analyzed, it was not difficult to find that, since the eastward and westward optical fibers of No. 3 NEwere connected reversely, No.3 NEtraced the clock of No.4 NEactually, and No.4 NEalso traced the clock of No.3 NE, as a result, the clocks were locked mutually, the clock performance of No.3 and No.4 NEs were deteriorated, and pointer justification and bit error occurred
In a certain office, SBS155 equipment is employed in local network to form two-fiber unidirectional path protection ring, the network structure is as illustrated in Fig 3-2. No.1 NEis the service central point and gateway NE, the respective NEs only exchange service with No.1 NE. The clock of No.1 NEis inter clock source, and other respective NEs all trace westward liNEclock.