How to perform a loopback test?

A loopback test serves to eliminate unnecessary connections and verify the proper functioning of a transceiver or port by connecting the transmitter and receiver within the same module. This test can be carried out using a self-contained loopback module or a single strand of fiber. However, when using a duplex cable, a few additional steps are required to create a single strand of fiber.

1. Select Cabling

2. Remove collar and isolate both ends of the same strand of cable

Here's a step-by-step guide on performing and confirming a loopback test using a single strand of fiber:

1. Insert the transceiver or loopback module into the switch. If you're testing a module with a reach of 40km or more, make sure to use the appropriate optical attenuator.
2. If you're using a loopback module, connect the Tx (transmit) and Rx (receive) ports to each other. If you're using a transceiver, connect the isolated ends of the same strand of cabling to the transmit and receive ports of the transceiver.
3. Once the ports are connected, observe the status of the link light. If it is illuminated, it indicates that the hardware port is functioning correctly. If the light is not lit, further troubleshooting steps are required.

Self-contained loopback module

Loopback created with single fiber strand

In conclusion, a loopback test provides a simple method to verify the proper functioning of your current hardware. While there are other factors to consider, such as cabling, connection points, and other network appliances, this technique allows you to eliminate those factors and confirm the functionality of your hardware.