This certifies whether the cable meets specifications in the part of the frequency spectrum where the signal mostly resides. For Category 3 links, the frequency test range is 1 MHz through 16 MHz. The cable tester will report a passing grade if all frequencies pass specifications. If a cable fails, the tester will tell you the frequency at which it didn't meet requirements. Some testers also indicate the amount of attenuation per foot.
Cable testers are available that work with metallic or fiber.
Current flow, resulting from the difference of potential impressed by the data signal, is electrons that move through a metallic wire. This stream of electrons creates an electromagnetic field around the wire that may induce the flow of electrons in an adjacent wire. This crossing of the signal into a different wire is called crosstalk. You may experience voice signal cross talk while talking on the phone. For example, you may hear another person's conversation while you're talking to someone else.