Imagine that you have been troubleshooting a network cable (either copper or fiber optic), and you determine that there is a break in the cable. What would you use to identify exactly where the break exists?

Question

A) Throughput tester
B) Punch-down tool
C) Toner probe
D) Time domain reflectometer

Answer 1

D
Explanation: Imagine that you have been troubleshooting a network cable (either copper or fiber optic), and you determine that there is a break in (or physical damage to) the cable. However, identifying exactly where the break exists in a long length of cable can be problematic. Fortunately, you can use a time domain reflectometer (TDR) for copper cabling or an optical time domain reflectometer (OTDR) for fiber-optic cabling to locate the cable fault. Both light and electricity travel at speeds approaching 3 * 108 meters per second (approximately 186,000 miles per second), although the speeds are a bit slower and vary depending on the medium. A TDR can send an electric signal down a copper cable (or an OTDR sends light down a fiber-optic cable), and when the electric signal (or light) encounters a cable fault, a portion of the electric signal (or light) reflects back to the source. Based on the speed of electricity, or light, in the medium and on the amount of time required for the reflected electric signal or light to be returned to the source, a TDR or an OTDR can mathematically determine where the cable fault lies.