| 单词 | NEXT (Near-End CROSS Talk) |
| 释义 | NEXT (Near-End CROSS Talk) The unwanted coupling of energy between two circuits or chan- nels occurring at the near end of the link, that is, at the end closest to the point of signal origin. Since at that point the outgoing downstream signal is at maximum strength and the incoming upstream signal is at minimum strength, the signals can couple quite easily if the attenuation-to-crosstalk ratio (ACR) is not maintained at acceptable levels. NEXT is a particularly significant issue at the network side of the connection for V.90 modems and ADSL services, as the pair count of the cables is quite high at the central office (CO) and, therefore, there are many opportunities for co-channel interference. However, ACR can be managed much more effectively at the edge of the telco network than at the customer premises. Far-end crosstalk (FEXT) occurs at the far 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, FEXT, signal, upstream, and V.90. |
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