Services on SNCP Rings Become Unavailable due to Fiber Misconnections

Services on two SNCP rings become unavailable due to fiber misconnections. This problem is solved by reconnecting the fibers.

Product

OptiX OSN 3500, OSN 2500, OSN 7500

Fault Type

SNCP fault

Symptom

NE C (the OptiX OSN 3500) forms two 155 Mbit/s SNCP rings with two groups of STM-1 optical interfaces. Ring 1 connects NE A (the OptiX Metro 1000) and Ring 2 connects NE B (the OptiX Metro 1000). NE A and NE B send 2 Mbit/s services respectively to port 1 and port 2 on NE D. Figure 1 shows the network diagram.

Figure 1 Correct SNCP network diagram

After the fibers on Ring 1 and Ring 2 are cut over, NE C does not report any alarm or performance event. The services on Ring 1 and Ring 2, however, are interrupted.

Cause Analysis

Possible causes of the problem are as follows:

• The services are incorrectly configured.
• The loopback of services is not released.
• Fibers are misconnected.

Procedure

1. Check the service configuration and confirm that the service configuration is correct. In addition, the cutover does not change the services.
2. Perform an outloop respectively at the tributary ports on NE A, NE B, and NE D. The outloops are normal, indicating that the NEs are connected properly.
3. Perform an inloop for the 2 Mbit/s services on NE A and test the signals at Port 1 on NE D. The test reports the OOF alarm.
4. Deactivate the services that NE D receives from NE B. As a result, the APS switching occurs on NE A. In addition, the services on NE A recover. It can be inferred that fibers are misconnected.
5. Check the fiber connections between NE A and NE C, between NE B and NE C by modifying the J0 byte. It is found that one pair of fibers on Ring 1 and one pair of fibers on Ring 2 are not connected as shown on the NMS. Figure 2 shows the incorrect SNCP network diagram.
   Figure 2 Incorrect SNCP network diagram
   
6. Reconnect the fibers according to the fiber connections before the cutover. Then, the fault is rectified.

Related Information

If the transport equipment does not report any alarm or performance event, the network is not necessarily normal on the transport side.

Therefore, after a cutover that involves fibers connections on the transport side, you need to carefully check the fiber connections and ensure that the fiber connections are the same as before the cutover.

Try to use meters for troubleshooting and judge based on the testing results of meters.

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