Degraded Signal

Description

Degraded signals can occur on either the ESU Uplink port or GPON OLT ports. This alarm indicates that the received optical signal level is too low on the ESU ports, or bit errors have crossed a threshold on the GPON ports.

Occurs on GigE and 10Gig facilities when the received optical power falls below a preset threshold on the SFP or XFP on the ESU faceplate. This threshold is designed to alarm approximately when the signal level is such that the BER would fall below the 10e-12 bit error rate.

A Degraded Signal alarm also occurs on GPON ONTs when the OLT has detected that the upstream bit error rate (BER) for an ONT becomes greater than or equal to the BER. This alarm is not service affecting typically but indicates that maintenance should be performed on the GigE optics to ensure the high bit error rate required for IPTV services. If the link actually fails, the port has a Gigabit Ethernet Physical Layer Failure, and the Degraded Signal alarm is masked.

The Degraded Signal alarm is Indicated by the Low Sig LED on the faceplates of the ESU card and the QOIU faceplates.

The physical characteristics of the SFP and XFP modules that have been tested and approved for use with the ESU are detailed below.

 The TX/RX power characteristics of the SFP and XFP modules that have been tested and approved for use with the ESUs are listed below.

Note: Tellabs recommends the use of a matching set of Tellabs approved XFP modules with Tellabs equipment and at the far end switch or router.

At +85°C to 95°C the ESU SFP/XFP module is capable of operating for a maximum of 450 hours per year. The maximum number of hours of continuous operation per day is 5 hours.

The GPON TX/RX power characteristics for the GPON SFPs are shown below:

Laser Safety

Warning! Personnel handling fiber optic cables must be trained for laser safety.

Warning! Optical Fibers emit invisible laser radiation. Avoid direct exposure to the beam. Never look into the end of a Fiber or into a Fiber connector on a cable or a device. Permanent eye damage or blindness can occur quickly from laser radiation.

Fiber Optic Cable

Ensure that the fiber connectors are properly cleaned per local standards. Dirty connectors may result in inaccurate measurements.

Caution: Fiber optic cable installation and maintenance should only be performed by trained service personnel.

Caution:  Do not bend the fiber optic cable to a diameter smaller than 7.5cm/3 inches. Doing so may damage the fiber or prevent the signal from passing through properly.

Trouble Clearing

The probable causes of this alarm are: 

• Improperly Seated Connectors: One cause of a Degraded Signal alarm is the connector not being properly seated. Ensure that all fibers are properly seated into their mated connector.
• SFP or XFP beginning to fail: As the optical SFP and XFP devices begin to age and fail, they may begin to have Degraded Signal alarms on the far-end system.
• Dirty Fibers: If not properly maintained, dirt and dust may have accumulated on the fiber connectors which can attenuate the signal causing bit errors on the fiber.
• Distance Too Long: If this is a new installation, it is possible that the distance rating of the SFP/XFP has been exceeded. Check the SFP/XFP type and the fiber type and optical budget to ensure that the distance is within specification.
• Fiber Problem: The fiber may have been bent or stressed and may have been damaged.
• ONT Problem: It is possible that the ONT has a hardware problem that is causing the bit errors. The alarm is cleared when the upstream BER for the ONT becomes less than the BER maintenance threshold.
• GPON Degraded Signal: Use the GPON Optical troubleshooter (refer to GPON Optical Troubleshooter) to diagnose and correct an issue with the GPON.
• ESU Degraded Signal: Use the ESU Optical Troubleshooter (refer to ESU Optical Troubleshooter3) to diagnose and correct an issue with the system.