This document discusses troubleshooting copper wire networks. A bad cable is one that falls outside specifications, such as exceeding maximum length. Common copper wire problems include mismatched termination standards between devices, split pairs during termination, and transmit/receive reversals. The TIA/EIA created termination standards T568A and T568B to reduce problems and ensure consistency.

1. Troubleshooting
copper wire
networks II.

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 User Training
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PACE-IT.
– What constitutes a bad cable?
– Common copper wire problems.

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Troubleshooting copper wire networks II.

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Network cables can go bad,
or be bad, without any
visible indication.
Additionally, a cable may be
inappropriate for a
particular application.
Anything that makes a cable fall outside of
specifications will make it a bad cable. How long is
the cable? Is the cable over its maximum run length?
Is the cable rated for the amount of data being run
over the wire? All of these, plus more, can constitute
a bad cable.
By using the proper tools and methodology, a bad
cable can be identified and any problems associated
with the bad cable can be rectified.
Troubleshooting copper wire networks II.

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Troubleshooting copper wire networks II.
– Copper wire termination standards.
» The TIA/EIA (Telecommunications Industry
Association/Electronics Industry Alliance) has developed a set
of termination standards for twisted pair copper wire.
• The standards ensure that network transmission is consistent
across networks.
» The standards involve how the pairs of wires are ordered when
placed in the termination device—usually either an RJ45 or
punchdown block.
» The current termination standards are:
• T568B: white orange-orange, white green-blue, white blue-
green, white brown-brown.
• T568A: white green-green, white orange-blue, white blue-
orange, white brown-brown.
» Not following the standards may lead to network problems.
• Cable testers and certifiers can be used to determine if a
twisted pair copper wire network cable meets the standards.

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Troubleshooting copper wire networks II.

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Troubleshooting copper wire networks II.
– Twisted pair termination standards.
» A straight-through cable is used to connect different types of
devices (e.g., a computer to a switch, or a switch to a router).
• Both ends of the cable are terminated to the same standard.
» A crossover cable is used to connect similar types of devices
(e.g., a computer to a computer, or a switch to a switch).
• One end will be terminated to the T568A standard and the
other end will be terminated to the T568B standard.
– Mismatched cabling standards.
» Using the wrong type of cable (e.g., using a straight-through
cable when a crossover cable is specified) can lead to network
problems.
• Many IT devices use a process called auto-MDI/MDI-X in
which they can auto-sense the type of device on the other end
of a cable and electronically change their send/receive setup
to match the cable used. Reliance on this may contribute to
the problem.
» Cable testers can be used to help identify the problem.

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Troubleshooting copper wire networks II.
– Split pairs.
» The problem occurs during the termination process.
• At least two pairs of wires that should be grouped together in the
termination device (e.g., the RJ45 or punchdown block) get
separated.
» The problem may not be identifiable with the most basic of cable
testers.
• If the split pairs are due to a misunderstanding of the termination
standards, it may still test as a straight-through or crossover
cable. This often leads to a crosstalk issue.
• A good cable certifier can identify the problem.
– Tx/Rx (transmit/receive) reverse.
» A PC type device uses pins 1 and 2 (one pair of wires) to transmit
a signal and pins 3 and 6 (another pair of wires) to receive a
signal.
• The receiving device must be configured to either receive on
pins 1 and 2 and transmit on pins 3 and 6 or the proper cable
must be used. If not, the link will not be created—Tx/Rx reverse.
» If the link fails to be created, check the pinout on the cables to
ensure that a Tx/Rx reverse has not occurred.

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Troubleshooting copper wire networks II.
Anything that makes a network cable fall out of its specifications constitutes
a bad cable. The TIA/EIA created a set of specifications on how to
terminate twisted pair copper wire—the T568B and T568A standards.
Following these standards will help to reduce the probability of copper wire
network problems.
Topic
What constitutes a bad
cable?
Summary
A straight-through cable is terminated to the same standard on both ends. A
crossover cable is terminated to the T568A standard on one end and the
T568B standard on the other. Mismatched termination standards can lead
to problems in network communication. Split pairs can still test as good but
lead to problems with crosstalk. A Tx/Rx reverse problem will prevent a
transmission link between devices.
Common copper wire
problems.

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