The External Clock Source Is Unavailable After a Fiber Cut Because the Clock Configuration Is Incorrect

The priorities of the clock sources are set incorrectly, so the external clock source is unavailable after a fiber cut. After the priorities of the clock sources are re-set, the fault is rectified.

Product

OptiX OSN 7500, OSN 3500, OSN 2500

Fault Type

• Bit errors
• LTI

Symptom

The EOW board on NE A is connected to two clock sources from third-party equipment, the network clock tracing is normal. After a fiber cut occurs on the ring network, the external clock source becomes unvailable. In addition, NE D reports the LTI alarm, and a large amount of bit errors occur.

Cause Analysis

In normal cases, the working path of the clock tracing is external clock source->NE A->NE B->NE C->NE D->NE F; the protection path is external clock source->NE A->NE F->NE D->NE C->NE B. After a fiber cut occurs on the ring network, the clock source of NE D is lost. After the clock configuration of the network is checked, it is found that System Clock Source Priority Table on NE D is not configured.

Procedure

1. Query the clock subnet configuration by using the NMS.
   1. In the NE Explorer of NE D, choose Configuration > Clock > Clock Subnet Configuration.
   2. Choose the Clock Quality tab, and Choose the Clock Source Quality. Click Query. The return shows that the system receives the G.811 primary reference clock (PRC) from the 11-SL64 board.
   3. Choose View > Clock View to obtain the clock tracing relationship of NE D. The west clock source (on NE C) next to NE D is unavailable, so NE C should trace its east clock source.
2. In the NE Explorer of NE D, choose Configuration > Clock > Clock Source Priority. Then, select Priority Table for Phase-Locked Sources of 2nd External Clock Output, and click Create to add 8-SL64 and 11-SL64 as clock sources.
3. In the Clock View, refresh the clock tracing relationship. Then, the alarm clears.