4.2 Signals and Noise  
  4.2.5 Cable testing standards  
The TIA/EIA-568-B standard specifies ten tests that a copper cable must pass if it will be used for modern, high-speed Ethernet LANs. All cable links should be tested to the maximum rating that applies for the category of cable being installed.

The ten primary test parameters that must be verified for a cable link to meet TIA/EIA standards are:

  • Wire map
  • Insertion loss
  • Near-end crosstalk (NEXT)
  • Power sum near-end crosstalk (PSNEXT)
  • Equal-level far-end crosstalk (ELFEXT)
  • Power sum equal-level far-end crosstalk (PSELFEXT)
  • Return loss
  • Propagation delay
  • Cable length
  • Delay skew

The Ethernet standard specifies that each of the pins on an RJ-45 connector have a particular purpose. A NIC transmits signals on pins 1 and 2, and it receives signals on pins 3 and 6. The wires in UTP cable must be connected to the proper pins at each end of a cable. The wire map test insures that no open or short circuits exist on the cable. An open circuit occurs if the wire does not attach properly at the connector. A short circuit occurs if two wires are connected to each other.

The wire map test also verifies that all eight wires are connected to the correct pins on both ends of the cable. There are several different wiring faults that the wire map test can detect. The reversed-pair fault occurs when a wire pair is correctly installed on one connector, but reversed on the other connector. If the orange striped wire is on pin 1 and the orange wire on pin 2 at one end, but reversed at the other end, then the cable has a reversed-pair fault. This example is shown in the graphic.

A split-pair wiring fault occurs when two wires from different wire pairs are connected to the wrong pins on both ends of the cable. Look carefully at the pin numbers in the graphic to detect the wiring fault. A split pair creates two transmit or receive pairs each with two wires that are not twisted together.

Transposed-pair wiring faults occur when a wire pair is connected to completely different pins at both ends. Contrast this with a reversed-pair, where the same pair of pins is used at both ends. Transposed pairs also occur when two different color codes on punchdown blocks, representing T568-A and T568-B, are used at different locations on the same link.

 

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