Content









12.1

Hardware Terms, Concepts, and
Components



12.1.5

Hardware monitoring devices





Most hardware devices that are used for
network monitoring and management are merely dedicated computers that
run proprietary protocol analysis or network management software.
These are often portable computers. Some devices that can be useful in
troubleshooting network problems include the following:
Tone generator/locator (fox and
hound)
The łfoxę portion can be attached to one end of the cable, and a
tone is generated. A locator, or the łhoundę, at the other end
receives the tone. This shows that the correct cable has been
identified. Figure
shows an
example of the fox and hound.
Crossover cable
The crossover cable is an Ethernet Unshielded Twisted-Pair (UTP)
cable in which two of the wire pairs are crossed. Normally in UTP, pin
1 connects to pin 1 on the other end, pin 2 connects to pin 2, and so
on. With the crossover cable, pins 1 and 2 connect to pins 3 and 6 on
the opposite end, and pins 3 and 6 connect to pins 1 and 2. The
crossover cable is used to connect two computers without going through
a hub. It is also used to connect two hubs when there is no uplink
port. Figure
shows the
coloring scheme for one end of a crossover cable.
Time domain reflectometer (TDR)
With a TDR, a sonar-type pulse is sent through the cable. The
pulse is measured to locate shorts or breaks in the cable. Figure
provides
examples of typical TDRs.
Hardware loopback
This device is connected to the serial port to send data, which is
then "looped back" to be received by the same computer. This makes a
test of the serial port possible without a modem or other device
attached to the computer.
Digital volt-ohm meter
The volt-ohm meter, or voltmeter, is used to measure electronic
pulses through cable and to determine if there are shorts or breaks in
the cable. Figure
shows an
example of a digital volt-ohm meter.
Cable tester
A cable tester is used to detect breaks and shorts. An advanced
cable tester can display additional information about the cable
condition and properties. Figure
shows an
example of a cable tester.
Oscilloscope
An oscilloscope is used in electronics calibration. It is also
used to measure the signal voltage that passes through a cable. The display is output to a small monitor as a
waveform. This can show attenuation caused by shorts or crimped wires
in the cable. Figure
shows an
example of an oscilloscope.
LAN meter
A LAN meter can check for broadcasts, collisions, usage levels,
and errors on Ethernet and Token Ring LANs. It can measure throughput
across WANs. A LAN meter also can identify devices connected to the
network. Figure
shows an
example of a LAN meter.