Troubleshooting Fiber Optic Links

About this task

You can troubleshoot fiber optic links to ensure that the optical transmitters and receivers operate correctly, and to determine if a receiver is saturated, or does not receive enough power.

To troubleshoot optical links and devices, you can use Digital Diagnostic Monitoring (DDM), as well as published optical specifications.

For more information about transceivers, see Extreme Networks Pluggable Transceivers Installation Guide.

Important

As a best practice, use transceivers documented in Extreme Networks Pluggable Transceivers Installation Guide, as they have been through extensive qualification and testing. Extreme Networks is not responsible for issues related to third party transceivers.

Procedure

Measure the transmit power.
Compare the measured transmit power with the specified launch power.

The values are similar. If the measured power is far below the specified value, a faulty transmitter is a possible cause.
Compare the measured transmit power for the near-end optical device to the measured transmit power for the far-end device.

Large differences can mean that the optical devices are mismatched (that is, -SX versus -LX).
Measure the receive power at each end of the link.
Compare the receive power to the transmit power.
- For short fiber links, the transmit and received power are similar (after taking into consideration connection losses).
- For long fiber links, the transmit and received power are similar (after taking into consideration connection losses and fiber attenuation).
Large differences can mean a damaged fiber or dirty or faulty connectors. Large differences can also mean that the link does not use the right type of fiber (single mode or multimode). If the receiver power is measured to be zero, and the link worked previously, it is probable that the far-end transmitter is not operating or the fiber is broken.
Compare the measured receive power for the near-end optical device to the measured receive power for the far-end device.

Large differences could mean that the optical devices are mismatched (that is, -SX versus -LX). If optical devices are mismatched, the receiver can be saturated (overdriven).
If a receiver is saturated but still operable, install a suitable attenuator.

For long-haul optical devices, the receive power must be significantly less that the transmit power.
To help debug the link, loop back the local transmit and receive ports, and use the DDM parameters to help determine the fault.