FEXT Definition


The unwanted coupling of energy between two circuits or channels occurring at the far end of a link, i.e., far away from the point of signal origin. It is at the far end that the attenuated downstream signal from the network, for can experience crosstalk from the strong upstream signal emanating from equipment at the customer premises. FEXT is not a large issue for V.90 modems or asymmetric digital subscriber line (ADSL) services at the customer premises, as the cables are successively smaller, containing fewer and fewer twisted pairs, from the central office (CO) to the premises, so there are fewer opportunities for signals to experience co-interference. Near-end crosstalk (NEXT) occurs at the near end of the link. It is in consideration of the phenomenon of crosstalk and the differences between NEXT and FEXT, that V.90 modems and most DSL services are asymmetric, with the higher frequencies on the downstream side (i.e., from the edge of the telco network to the customer premises) in support of greater bandwidth in that direction. See also ADSL, asymmetric, bandwidth, channel, circuit, CO, crosstalk, downstream, frequency, interference, link, NEXT, signal, upstream, and V.90.

Webster's New World Telecom

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