Methods for testing optical path bit errors during the acceptance of WDM devices

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1. During the system commissioning of devices in back-to-back mode, use pigtails to respectively connect the Rx and Tx ports of the TQX board on the front subrack to the Tx and Rx ports of the corresponding board on the rear subrack.
2. Connect the Rx and Tx ports of the TDX board in the rear subrack at the central site to form a loopback.
3. Connect test instruments to the TI and RO ports of the TDX board on another subrack at the central site to cover most of the paths after the 24-hour bit error test.
4. If another wavelength needs to be tested, connect multiple wavelengths according to the SDH connecting method.

Other related questions:
Relationship of the optical power, sensitivity, and bit errors
Relationship of the optical power, sensitivity, and bit errors: When the optical power is lower than the receiver sensitivity, bit errors do not necessarily occur. However, you are advised to adjust the optical power to the normal range as soon as possible.

ECC bit error introduction and query methods
Question: What are ECC bit errors? Analysis: There are two types of ECC bit errors: ECC bit errors on line boards and ECC bit errors on system control boards. The ECC bit errors on line boards are errors in the overheads of received SDH frames. You can query these bit errors from historical performance data. The ECC bit errors on system control boards are errors that are generated when the system control boards receive signals. Answer: Run the cm-get-chanerror command for at least 30 times at an interval of 10 seconds. In the command output, the fields LG, NO, CR, AB, UN, and MRF indicate bit errors. If these fields increase continuously during the query, bit errors are generated; otherwise, no bit error is generated. Suggestion and conclusion: You can query ECC bit errors to determine whether the unreachability of an NE is caused by ECC bit errors.

Service bit errors
Question: What may cause service bit errors? Analysis: None Root cause: None Answer: 1. Unreasonable dispersion compensation (not enough or too much); 2. Too high or too low incident optical power; 3. Performance deterioration of the transmit laser on the OTU board at the transmit end; 4. Severely contaminated pigtail connectors; 5. Changes in fiber attenuation; 6. Performance deterioration of the receive laser on the OTU board at the receive end. Suggestion and conclusion: None

Relationship between the optical power of a line board and bit errors
Relationship between the optical power of a line board and bit errors: Bit error events may occur when the receive optical power of a line board exceeds the upper or lower threshold. If bit error events occur when the receive optical power is between the lower threshold and the upper threshold, the possible causes are as follows: The fiber quality deteriorates, the line board is faulty, or the connector is dirty.

Method used to query bit errors based on logs
You can query bit errors based on logs as follows: If you cannot log in to a remote device, collect logs and analyze them. 1. Bit error of a SAS port Analyze the message log. a. Determine the failure time based on the Event.txt log. b. Query the message log that corresponds to the failure time and search keyword bit err overflow disable. Possible Cause A cascading SAS cable is insecurely connected. A cascading SAS cable is contaminated. A cascading SAS cable is damaged. Troubleshooting a. Check events. If the cascading SAS cable has been removed and inserted before the failure, the cable may be insecurely connected. b. Remove and insert the cable to check whether more bit errors are displayed. If no more bit error is displayed, the previous bit error is caused by insecure connection. If bit errors continue to display, replace the cascading SAS cable. c. If spare cascading SAS cable is available on the site, replace the faulty cable. Otherwise, apply for a spare cable. 2. Bit error of a Fibre Channel port The FC loop feature may lead to multiple possible bit errors. To analyze the spreading status of Fibre Channel bit errors, you must confirm the networking mode and the spreading direction of the bit error based on the SES log. During fast locating, you only need to pay attention to SES logs. Keywords: HD Format of the bit error log: HD: [Port ID:Number of LCV bit errors:Number of CRC bit errors] a. Bit errors of a disk b. Bit errors of a link Possible Cause Connection of Fibre Channel cables Optical fiber fault Optical module fault Troubleshooting Remove and reinsert the optical fiber. If no more bit error is displayed, the fault is caused by insecure connection. Replace the optical fiber. If no more bit error is displayed, the fault is caused by the optical fiber failure. Replace the downstream optical port. If no more bit error is displayed, the fault is caused by the downstream optical port failure. Replace the upstream optical port. If no more bit error is displayed, the fault is caused by the upstream optical port failure.

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