One particular type of cabling issue is the one in which the Transmit and the Receive pairs of a cable are inversed so the TX sides are connected to each other and the RX sides are connected to each other (as opposed to the correct way of connecting TX to RX).
In an Ethernet environment, this can lead to a straight-through cable being transformed into a crossover cable, and vice versa. This scenario is easy to identify and might not be an issue if the devices can automatically detect and correct this. This functionality is called auto-sensing or auto-MDIX and is transparent to the user.
The mistake can be at the connector or somewhere in the patch panel, and this is usually a human error. Because the error is not somewhere inside the cable, it can be relatively easy to identify by visually analyzing the cable terminations.
These types of issues are also present in optical fiber installations and can come in two forms:
- The cable has dedicated TX and RX connectors that are inserted into the wrong ports on the device
- The cable has a single connector (with both TX and RX fiber strands) that is incorrectly crimped (TX at one side of the cable to RX on the other side of the cable)
Solutions to fixing reversed TX/RX issues include:
- Changing the connector
- Changing the patch panel termination
- Inversing the RX and TX connectors (i.e., optical fibers)
Just like in other types of cabling issues, to find the exact problem and location, you can use dedicated diagnostic equipment (e.g., wire mapping devices) that can provide accurate results on the cable and connector configurations.