What Is Crosstalk?

Date First Published: 18th May 2022

Topic: Computer Networking

Subtopic: Data Transmission Technologies

Article Type: Computer Terms & Definitions

Difficulty Level: 6/10

Learn more about what crosstalk is in this article.

Crosstalk is the interference between cables in another circuit or channel, caused by signal transmission issues. It occurs when the signal that is transmitted on one twisted-pair cable interferes with and reduces the quality of transmission for the other pair. It is usually caused by the cables running too closely together, causing the signals from one cable to get mixed up. This might cause the receiver to hear someone else’s conversation from a telephone line.

The term 'crosstalk' was invented in the early days of the Public Switched Telephone Network. Some cables use shielding to reduce the effects of crosstalk and it can be prevented by not running cables directly near each other.

Note:

It is called crosstalk because the disruption to the signal causes the signals to become confused and 'cross over' with each other.

Types Of Crosstalk

Types of crosstalk include:

Near-end crosstalk (NEXT)

NEXT crosstalk refers to signal interference in wire pairs next to each other within the twisted-pair cable at the near-end of the link. When NEXT crosstalk occurs, an outgoing data transmission leaks over to incoming data transmission, causing the incoming transmission to overhear the signal sent by the transmitter at the near-end of the link. NEXT occurs at the transmitter side rather than the receiver side.

Far-end crosstalk (FEXT)

FEXT crosstalk refers to crosstalk that occurs at the far end of the transmitter or the point where the signal originated from. This type of crosstalk is worse as the signal has already travelled a distance and carries some unwanted signals. FEXT adds more unwanted signals and is measured in decibels.

Power sum near-end crosstalk (PSNEXT)

PSNEXT is a calculation that adds up the NEXT measurement of all pairs of wires that are next to each other. It involves measuring all pair-to-pair crosstalk groupings and then adding up all of the values for every pair. The unit of PSNEXT is measured in decibels. The total disruption that is faced by a signal will be equivalent to the number of disruptions created by all other pairs of cables that are next to each other.

Alien crosstalk (AXT)

AXT refers to signal interference that occurs in a cable that runs alongside several other cables that corrupt the signal of the cable. The term ‘alien’ means that this type of crosstalk occurs between various cables in a bundle or group rather than single wires or circuits within a single cable.