Loopback Tests and Media Converters

| 5/17/2016 12:00:00 AM

loopback is a mechanism through which a message or signal ends up (or loops) back to where it started. A loopback can be a hardware or software-based test. The most important purpose of the test is to discover whether there is a physical connection fault, and to identify the segment that contains the fault.

Serial Devices
Serial devices using RS-232/422/485 may require a terminal emulator program to perform the test. T1 Media Converters, for example, installed in a Telecommunications environment, can be set into a loopback mode to test each segment of the connections, including both the copper and fiber connections.

Copper to Fiber Media Converters

To test a media converter by itself, start by making sure that you have an appropriate fiber patch cable.

Step 1: Connect the media converter to the twisted pair device with a twisted pair cable.  Make sure to connect it to an RJ-45 port on a device of the same speed capability. Once you achieve a link LED on the copper port, proceed to step 2.

Step 2: Loop a single strand of fiber from the transmit port to the receive port of the media converter. If using a dual strand fiber patch cable, connect one strand to the XMT port of the media converter and one strand from the OTHER END to the RCV port.

Step 3: If the fiber port LED lights, you can verify that the device is working properly.  If the fiber LED does not light, assume that the media converter is broken.

Make sure to use the appropriate CAT 5 or higher copper cable.  If your media converter does not include AutoCross, make sure that the crossover/pass-through switch is set correctly,.

We often receive a desperate call at the end of a business day, after an installer has spent all day trying to figure out what is wrong with a network installation. The first product he will look at is the Ethernet media converter. By following  the simple steps listed above, he can find out whether the media converter is a problem at the physical level.

If the media converters prove to have valid link LEDs, then the network admin or installer must start looking at other equipment, as well as assessing what types of equipment he is connecting, in terms of speed and fiber type.

Advantech B+B Smartworx tech support personnel can provide troubleshooting advice and help you resolve possible issues quickly. Industrial networking can be complex -- it’s great to have friends that you can rely on.


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