When analyzing a connector (e.g., an RJ45 Ethernet connector), you should carefully inspect the following aspects:
- Verify that it is correctly crimped, including the order of wires
- Verify that all wires are touching the metal connector blades and that the crimp is not partial
- Verify that no wires are missing
- Verify that the plastic cable jacket is fixed into the connector (i.e., wires are not hanging out of the connector)
- Verify that the RJ45 lock is functional on the connector (otherwise, the connector will pop out of the port)
Generic wire problems are usually called short circuits. However, cable issues involve both short circuits and open circuits, which are completely opposite problems. A short circuit involves two wires within a cable or connector touching each other. In a normal operation mode this should not happen, as each wire in a cable is isolated inside a shell to prevent interaction with the other wires as it transmits an independent signal. If two wires do touch, the signals associated with each of them will cross from one to the other, causing a lack of signal.
The recommended way to investigate cable issues is using cable testing equipment that can work with copper or fiber cables. Such devices can provide advanced results, such as:
- Which wire has the problem
- What the problem is
- How far the problem is (location between endpoints)
The amount of signal loss depends on a number of different criteria, including:
- Distance
- End connectors
- Cable quality
- Patches between the endpoints
- Electrical interference (for copper cables)
- Radio interference (for wireless traffic)
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).
Once the cables are installed, you have to make sure that they are protected from electromagnetic interference (EMI) or other types of interference that could cause problems with the signal that travels through the cable.