Networking / Beginners

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Crosstalk

Whether its coaxial cable, or UTP, copper-based cabling is susceptible to crosstalk. Crosstalk happens when the signal from one cable gets mixed up with the signal in another cable. This can happen when cables run too closely together. Some cables use shielding to help reduce the impact of crosstalk. If shielded cable is not used, cables should not be run directly near each other.

Near-End Crosstalk (NEXT)

NEXT refers to interference between adjacent wire pairs within the twisted-pair cable at the near-end of the link (the end closest to the origin of the data signal). NEXT occurs when an outgoing data transmission leaks over to an incoming transmission. In effect, the incoming transmission overhears the signal sent by a transmitting station at the near end of the link. The result is that a portion of the outgoing signal is coupled back into the received signal.

Far-End Crosstalk (FEXT)

FEXT occurs when a receiving station overhears a data signal sent by a transmitting station at the other end of a transmission line. FEXT identifies the interference of a signal through a wire pair to an adjacent pair at the farthest end from the interfering source (the end where the signal is received).

Electromagnetic interference (EMI)

Electromagnetic interference (EMI) can reduce signal strength or corrupt it altogether. EMI occurs when cables are run too close to everyday office fixtures such as computer CRT monitors, fluorescent lighting fixtures, elevators, microwaves, and anything else that creates an electromagnetic field. Again, the solution is to carefully run cables away from such devices. If they have to be run through EMI areas, shielded cabling or fiber cabling needs to be used.

Attenuation

All media has recommended lengths that the cable can be run. This is because data signals weaken as they travel farther from the point of origin. If the signal travels far enough, it can weaken so much that it becomes unusable. The weakening of data signals as they traverse the media is referred to as attenuation. All copperbased cable is particularity susceptible to attenuation. When cable lengths have to be run farther than the recommended lengths, signal regenerators can boost the signal as it travels. If you work on a network with intermittent problems and notice that cable lengths run too far, attenuation can be the problem.