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A collection of technical terms and abbreviations.

Technical terms

  • Attenuation - The amount by which the signal level is reduced over its path from one point to another. In the context of broadband, this means the reduction in signal level over the length of the telephone line.
  • Downstream - Refers to the movement of data towards the user from a remote location.
  • Modem/router - A device which combines a DSL modem and a router in a single package. Most modem/routers also include a network switch and a firewall, to make them into an all-in-one solution for internet access.
  • Noise margin - The amount by which the SNR exceeds a specified base level of SNR. In a DSL connection, the base level of SNR is the level below which a stable connection is not likely to be possible.
  • Router - A device which passes packets of data between networks. A router steers data to the correct destinations as specified in the packet headers. The term 'router' is often used loosely to refer to a modem/router.
  • SNR margin - See noise margin.
  • Upstream - Refers to the movement of data away from the user towards a remote location.


  • ADSL - Asymmetric Digital Subscriber Line. A protocol for broadband connections over telephone lines, in which greater provision is made for downstream data transfer than upstream.
  • dB - Decibel. A measure of gain or loss in a system. See Decibels in the context of ADSL
  • DSL - Digital Subscriber Line. A generic name for a group of technologies which enable the transmission of digital data over a telephone line.
  • FTTC - Fibre To The Cabinet. A hybrid arrangement for telephone lines; fibre-optic cable links the exchange to street cabinets, and copper cable links the cabinets to user premises. Used for BT Infinity and similar offerings from other ISPs.
  • FTTP - Fibre To The Premises. Fibre-optic cable links the exchange directly to user premises.
  • ISDN - Integrated Services Digital Network. A set of standards for simultaneous digital transmission of voice, video, data and other services over a telephone line. Used in some countries for internet access, but largely superseded by DSL.
  • LAN - Local Area Network. A network of computers and associated devices which is entirely within a limited area, such as a house, school or office building.
  • SDSL - Symmetric Digital Subscriber Line. A protocol for broadband connections over telephone lines, in which equal provision is made for downstream and upstream data transfer.
  • SNR - Signal to Noise Ratio. The signal level divided by the noise (interference) level. Usually expressed in dB.
  • VDSL - Very-high-bit-rate Digital Subscriber Line. A protocol for broadband connections over telephone lines, coaxial or fibre-optic cable.
  • VDSL2 - Very-high-speed Digital Subscriber Line 2. An enhanced version of VDSL, currently being employed on BT FTTC lines.
  • WAN - Wide Area Network. A telecommunications network which covers a broad area and links together several localities.
  • Wi-Fi or WiFi - A means of linking together electronic devices by wireless. Can be used within a LAN or to connect to a WAN by means of a hotspot.