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Chapter 3
Generic Troubleshooting Tools
Noise/interference
Wiring maps
MAC information
Line utilization
Time domain reflector (TDR)
It is important to realize that not all cable testers provide all of this informa-
tion. A given tester may provide only some of these attributes.
Time Domain Reflectors (TDRs) and Optical TDRs (OTDRs)
Time domain reflectors (TDRs)
are complex cable testers. They are used to
locate physical problems in a cable. They can detect where an open circuit,
short circuit, crimped wire, or other abnormality is located in a cable.
TDRs and Optical TDRs (OTDRs) work on the same principle: a signal is sent
down the cable and the unit waits for the reflected signal to come back. Different
abnormalities in cabling cause this signal to be reflected at different amplitudes.
Based on the signal strength, or amplitude, the meter distinguishes between opens,
shorts, crimps, or other failures in the cable. These meters measure the time
between the sending of the signal and the arrival of the reflected signal at the
unit. This time interval is used to calculate where the failure is occurring in the
cable. Optical TDRs can also provide information, such as signal attenuation,
fiber breaks, and losses through connectors.
Digital Interface Testing Tools
Digital Interface Testing tools consist of several different tools, such as
breakout
boxes
, used to verify pin-outs (e.g., TD--transmit data, RD--receive data,
CTS--clear to send) for all types of serial and parallel interfaces, and
bit/block
error rate testers
, used for testing the quality of a communication link based on
deviance from a known bit pattern. These tools are used to measure signals sent
from computer and communication equipment. They are also able to test
connections and communication between data terminal equipment and data
communications equipment.
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