Basic Cabling Testing
Troubleshooting Basics
7
7-27
Troubleshooting Basics
Troubleshooting LAN cabling installations is most often required during cabling
installation or modification. When cable is handled carefully and installed
correctly, it usually operates trouble-free for years.
A general rule for finding cabling faults is as follows: With very few exceptions,
faults occur at cabling connections. Cabling connections include
telecommunication outlets, patch panels, punchdown blocks, and transition
connectors.
Connections are the most likely places for faults for at least three reasons: (1)
Connections always alter the impedance of the transmission path, (2) connections
are likely places for faults caused by wiring errors and faulty or incompatible
hardware installation, and (3) connections always cause some crosstalk due to the
untwisting of cable pairs.
When cable is handled carelessly, faults can occur in the middle of the cable.
These faults can happen when the cable is stepped on, sharply bent, pinched by
cable ties or other hardware, or otherwise stressed.
A general procedure for finding cabling faults (excluding sources of noise and
traffic faults) involves the following steps:
1. Run an Autotest on the cabling.
2. If the Autotest fails, press F for specific information on the fault.
3. Inspect the cabling for the suggested fault at the location indicated by the
diagnostics display.
4. Repair any faults you find. To quickly check your repair, run the test that
failed as a Single Test.
5. Run the Autotest again to verify the cabling’s performance.
Table 7-1 on the next four pages shows examples of test tool displays for some
typical cabling faults.
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