Fiber optic cable breakage alarm between DU and RRU

A fiber optic cable break between DU and RRU triggers optical module alarms, typically indicating signal loss or high attenuation, which can be diagnosed and resolved through inspection, testing, and repair.

Causes of Fiber Breakage Alarms

Fiber optic alarms between a DU and RRU usually occur due to physical damage or connection issues in the optical link. Common causes include: Broken or severed fiber from external damage such as construction, excavation, or environmental stress (e.g., flooding, earthquakes). Excessive bending beyond the fiber's minimum bend radius, causing signal attenuation or breakage.

Dirty or misaligned connectors at the DU, RRU, or intermediate patch panels.

Faulty SF

P or optical modules in the DU or RRU.

Alarm Types

When a fiber break occurs, the RRU or DU may generate alarms such as: Optical Module Alarm: Indicates a problem in fiber communication between DU and RRU. Loss of Signal (LOS) or Loss of Tracking: Triggered when the optical signal is interrupted or synchronization is lost. External Alarm: May appear if the RRU is configured to monitor power or fiber link status.

Troubleshooting Steps

To resolve a fiber breakage alarm, follow these steps: Check Alarm Details: Use the Network Management System (NMS) to identify the affected ports and alarm type. Inspect Physical Connections: Verify that all fiber connectors are clean, properly seated, and free from damage. Test Fiber Continuity: Use an Optical Time-Domain Reflectometer (OTDR) or sweep tester to locate breaks or high-loss points along the fiber.

Restart Equipment: Power cycle the DU and RRU to see if the alarm clears. Replace Faulty Components: If the fiber is damaged, perform fusion or mechanical splicing to restore continuity. Replace defective SFP modules if necessary.

Verify TX/RX Connections: Ensure the transmit and receive ports are correctly connected and aligned. Clear Alarm: Once the issue is resolved, clear the alarm from the NMS and monitor the link for stability.

Preventive Measures

Regularly clean and inspect fiber connectors. Use weatherproofing and protective conduits for outdoor fiber runs. Avoid sharp bends and maintain proper minimum bend radius.

Monitor site temperature and power supply stability to prevent secondary alarms. By following these steps, network engineers can quickly identify the root cause of a fiber breakage alarm between DU and RRU and restore reliable optical connectivity.