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NEs Are Frequently Unreachable to the T2000 due to the Mutual Trace of the Clocks

Publication Date:  2019-07-05 Views:  117 Downloads:  0

Issue Description

The OptiX OSN 6800 NE is configured at the following stations: A (NE ID: x00/x01), B (NE ID: x02/x03), C (NE ID: x04/x05), D (NE ID: x06/x07), E (NE ID: x08), F (NE ID: x09/x10). The six stations form a ring network. Station A is the OLA station, and the other stations are back-to-back OTM stations. At station B, NE x03 in the direction of station C is often unreachable to the T2000 and NE x02 in the direction of station A also sometimes unreachable to the T2000. 

Alarm Information

The NEs at station B are often unreachable to the T2000.  

Handling Process

1. At station B, the field engineers log in to NE x03 on site by using an Ethernet cable. When the engineers log in to NE x02 through NE x03, the communication fails from time to time. When NE x02 functions as the gateway NE, the same symptom occurs after the engineers log in to NE x03.
2. Shut down the ESCs on the OTU boards in NE x02 and NE x03 and the ESCs on other NEs, so that the supervisory is transmitted through the OSC. As a result, the fault persists.
3. The engineers run :cm-get-eccroute; command to query the ECC routing information of NE x02 and NE x03. Only NE x02 or NE x03 is displayed in the routing table, and other NEs are not displayed.
4. The engineers run the :cm-get-bdinfo;, cm-get-chaninfo; and cm-get-chanerror; commands separately to query the ECC port information of NE x02 and NE x03. It is found that two ports on the 5-SC2 boards of NEs x02 and x03 have the CR error, and the errors increase gradually. In the query of the SC2 current performance data, it is found that the CRC4 bit error exists.
5. The engineers apply a self-loop at the optical interface on the 5-SC2 boards of NEs x02 and x03. Check whether the CR errors stop increasing. If so, the board is normal.
6. The engineers check the clock configuration on site through the T2000. Clocks are set on the entire network. According to the fiber connection relation provided by the engineering documents, the clock on NE x09 is set as internal clock, NE x09/x00/x01/x02/x03 traces the clock on NE x10, and the clock on NE x08/x07/x06/x05/x04 traces the clock on NE x10 from another direction.
7. The engineers apply a self-loop at the optical interface on the SC2. It is found that the actual fiber connections differ from the fiber connections specified in the engineering documents. Hence, the clock setting on the existing network is incorrect. The clocks at stations B and C trace each other. The clock setting for other NEs may be also incorrect. After a confirmation with R&D, it is found that the clocks on the OptiX OSN 6800 need not be set. After the clocks on the entire network are set on site to Internal on the T2000, the problem is solved. 

Root Cause

1. All OTU boards in the OptiX OSN 6800 support ESC. If the function of the ESC on an NE is unstable, the NE may be unreachable to the T2000. In this case, turn off the ESC on all the OTU boards and force the supervisory data to be transmitted through the OSC.
2. As the NEs at two directions of station B are unreachable to the T2000, and the two SC2 boards have the CR and CRC4 errors. The probability that SCC boards or SC2 boards on the two NEs are faulty is low. Thus, this is common problem on the NE.
3. If two clocks trace each other, the availability of the ECC cannot be ensured. The fiber connections shown in the as-built document differ from the actual fiber connections of the equipment. As a result, relevant clocks trace each other. This problem is detected only when a self-loop is configured on the SC2 on site. This makes the troubleshooting more difficult.
4. In general, the clock need not be configured for the OptiX OSN 6800. The clock on the entire network is set to the free-run mode. The clock trace source needs to be set only when the orderwire is configured.