Chapter 18: Network Troubleshooting Tools
Chapter Outline
1. On the Test
a. 4.5: Given a wiring task, select the appropriate tool (e.g., wire crimper, media tester/certifier, punch-down
tool, tone generator, optical tester, etc.).
b. 4.6: Given a network scenario, interpret visual indicators (e.g., link lights, collision lights, etc.) to
determine the nature of the problem:
2. General Tools
a. Every technician requires a set of tools to perform all of the tasks he will encounter while
troubleshooting network problems.
b. This set of tools can range from a screwdriver and pair of pliers to a fully stocked toolkit containing
specialized diagnostic equipment.
c. Technicians who perform the majority of their troubleshooting tasks in the field, or away from an office,
should consider some additional tools.
d. In addition, try to maintain a supply of spare parts.
3. Specialty Tools
Specialty tools are those that are used in special or peculiar circumstances.
4. Wire Crimper
a. Wire crimpers are used to attach terminals or connectors onto pieces of wire.
b. The head of the crimper contains indentations known as cavities. Once the terminator is slipped over the
wire, the jaws of the crimpers are opened and the terminator is slipped into the appropriate cavity. When
the handles are squeezed shut, the terminator is mashed onto the wire.
c. Correct cavity selection is critical and is based on wire size.
d. The cavities on most standard wire crimpers are color coded to correspond to wire size markings.
e. Crimpers are commonly used to connect coaxial cable with BNC connectors.
f. The cavities on coaxial crimpers are shaped in such a way that the actual crimp is made in a hex
configuration. This makes for a much more secure connection.
5. Media Tester
a. Media testers are used to test cable media, or, in plain language, network and telephone cables.
b. Most cable testers can be used to test both twisted pair and coaxial cable. Media testers can test and
confirm the actual wiring configuration for twisted pair cable to include whether or not the RJ-45
connectors are attached correctly.
c. With coaxial cable, the physical cable and termination can be tested.
d. Media testers work by sending an electrical signal down the length of the cable. Once the signal reaches
the other end, the quality and strength of the signal is evaluated.
e. Most common cable testers can be used to perform the following tests:
i. Continuity: Continuity testing is used to determine if a cable meets the electrical standards
identified by the manufacturer.
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ii.
Crosstalk: Crosstalk is noise that comes from adjacent wire pairs. Twisted pair
cable uses the twisted wires to help reduce the amount of crosstalk that occurs
between wires that are located near each other.
iii.
Noise: Electrical noise can be caused by a number of sources. Some of the most
common sources are electrical cables and fluorescent lights. Since this noise may
occur sporadically, line noise tests may need to be conducted over a period of
time to obtain accurate readings.
iv.
Attenuation: As a signal travels down a length of cable, it starts to lose its
strength. Attenuation checks can determine the amount of signal loss on a piece of
cable.
v.
Capacitance: Capacitance is measured in pF, or picofards per foot. This
measurement can tell you if the cable is kinked or if it has been stretched.
vi.
Time Domain Reflectometer (TDR): Time Domain Reflectometer (TDR) sends
an electrical signal down a length of cable, then records the amount of time it
takes for the signal to reflect back. TDRs are used to determine if the cable is
broken or has a short.
vii.
Cable Tracing: Tracing is used to trace the path a cable takes through a wall or
ceiling. Cable tracing uses a tone generator to send a signal through the cable.
While the tone is traveling through the cable, you can listen through the wall or
ceiling for the tone.
f. When purchasing a cable tester, be sure you pick one that meets the requirements of the cable type you
are testing.
6. Time Domain Reflectometer (TDR)
a. Time Domain Reflectometers (TDR) are a type of cable tester.
b. TDRs are used to determine if the cable is broken or has a short.
c. A TDR works by sending a signal to the end of a cable and then measuring the length of time it takes
for the signal bounce back.
d. If a cable is broken or has a short, the signal bounces back at a different speed or amplitude,
depending on the location of the defect.
e. TDRs are made for testing both copper and optical cables.
i.
Copper: With copper cables, the TDR sends an electrical signal down a length of cable, then
records the amount of time it takes for the signal to reflect back.
ii.
Optical: Optical time domain reflectometers (OTDRs) use reflected light to identify items
such as the length of the fiber optic cable, the location of cable breaks, and the effects of
attenuation.
7. Optical Tester
a. Optical testers are used to test fiber optic cabling systems by detecting reflected light.
b. By attaching probes to the optical fibers, items such as the output power of signal fibers and
attention can be measured.
c. Optical testers are commonly used to evaluate splices in the cabling system, connector joints, and to
locate faults.
8. Punch-Down Tool
a. Punch-down tools are used to attach telephone and data wires to punch-down blocks and patch
panels.
b. The actual tool is a hand-held device containing a plunger and cutter assembly.
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9. Tone Generator
a. Tone generators are used to trace problems in phone lines.
b. To use a tone generator, plug the RJ-11 connector from the tone generator into a modular telephone
jack. If working at the punch-down block, use alligator clamps to connect the generator directly to
the connectors or wires.
c. Turn the tone generator on to begin transmitting a signal down the length of the wire.
d. At the next junction of the wire, a tone probe is used to detect the tone.
10. Visual Indicators
a. Many devices have built-in lights that are designed to show you when a connection has been made
and when data collisions occur.
b. Some of the more common pieces of hardware that contain these types of lights are network
interface cards, hubs, switches, bridges, and routers.
11. Link Lights
a. Link lights are designed to demonstrate link connectivity at the physical layer. In simpler terms, that
means that a link exists between two network devices.
b. Link light status will vary from device to device.
c. In the event you are troubleshooting a network problem and you believe that connectivity may be the
problem, always check to see if the link light is lit. If not, check these items:
i. Trying to reseat the connection by unplugging the connection and plugging it back in.
ii. Unplug the cable from the other end; that is, the wall jack, hub, switch, etc., and reconnect it.
Inspect the cable and connector as outlined above. If the cable or connectors look questionable,
replace the cable.
iii. Restart the computer the workstation. Restarting should initialize the NIC, which may re-establish
the connection.
iv. At the hub or switch, check the corresponding link light. If it is not lit, plug the cable into another
port. If link connectivity is established, you will know the port on the hub was defective.
v. Check to make sure the hub or switch has power.
vi. If you are using a managed switch, check to see if someone has made changes to the switch
configuration, or if a port has been disabled.
vii. While at the hub, check the cable and connector just as you did at the workstation. Replace the
cable if you have any questions about its dependability.
viii. Use a cable tester to verify that all of the patch cables and network cable runs are operating
correctly.
ix. If a new patch cable has been installed, check to make sure it is not a crossover cable.
12. Collision Lights
a. Collision lights are used to detect collisions on an Ethernet network.
b. Whenever a device transmits data and a collision occurs, this light will glow.
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