When installing or repairing a network it is very important to be able detect and trace cables. There are three main ways to do this, tone tracing, continuity testing, and hub blinking. Each have their own set of unique features and limitations.
TONE - Tone tracing is one of the oldest and most common ways to detect any type of cable. However, ethernet cabling presents obstructions to this type of trace. If the tone is sent down two pairs on the same cable it will degrade along the length of the cable. This is due to a feature of the cable that decreases interference and minimizes noise on the line. For this reason, only one pair can be tested at a time. This makes tone tracing a very laborious way to detect cables. However, tone tracing is still the best way to locate a break in the line for repairs.
CONTINUITY - Most cable detection for ethernet cable is done through continuity testing. This process is capable of testing up to 20 cables at once and can speed up the process of mapping a network and labeling network connections. Unfortunately, this process will only show if a break in the line exists. It won't locate that break within the line.
HUB - One of the latest forms of cable detection is the hub blink method. Most network cards include a light that signals data transfer on the port. This light can be activated by a tool at either end of a cable in order to detect the other end. However, this method can only be used on networks that have been fully installed and is not viable for new networks that are still under construction.