Figure 1 shows a 4xVC-4 SDH ring configured with path protection (PP).
NE1 is the central station and the services of other stations are converged on NE1. The clock source of NE1 is the external clock source, and other NEs trace the west line clock source. The fiber between NE2 and NE3 is cut but the services are not interrupted. At this time, point adjustment performance events occur on NE1, NE3, NE4, NE5, and NE6. The PQ1 boards on NE1, NE3, NE5, and NE6 reports the PS alarm but no alarm is reported on NE4.
Check the fiber connection of NE4. It is found that the fibers are misconnected. After the fiber connection is corrected, the PQ1 board on NE4 reports the PS alarm.
Normally, the PQ1 boards on NE3, NE4, NE5, and NE6 should report the PS alarm if the fiber between NE2 and NE3 is cut. The PQ1 board on NE4 does not report the PS but the services are normal. The west line board on NE4 can normally receive services from NE1. Hence, the fiber connection of NE4 may be incorrect. That is, the west line of NE4 is connected to the west line of NE5 and the east line of NE4 is connected to the east line of NE3.