100BaseT. A 100-Mbps local area network that maintains backward compatibility with 10BaseT networks running at 10 Mbps.

10BaseT. A 10-Mpbs Ethernet local area network that runs over twisted pair wiring. This network interface was originally designed to run over ordinary twisted pair (phone wiring) but is predominantly used with Category 3 or 5 cabling.

access rate. The transmission speed of the physical access circuit between the end user location and the local network. This is generally measured in bits per second. Also called "access speed."

adapter card. Circuit board or other hardware that provides the physical interface to a communications network; an electronics board installed in a computer that provides network communication capabilities to and from that computer; a card that connects the DTE to the network. Also called a "network interface card" (NIC). See also data terminal equipment and network interface card.

ADSL Forum. The organization that develops and defines xDSL standards, including those affecting ADSL, SDSL, HDSL, and VDSL. On the Internet, visit at http://www.adsl.com/.

asynchronous transmission. Data transmission of one character at a time to the receiving device, with intervals of varying lengths between transmittals, and with start bits at the beginning and stop bits at the end of each character, to control the transmission. In xDSL and in most dial-up modem communications, asynchronous communications are often found in Internet access and remote office applications. See also synchronous transmission.

ATM. Asynchronous Transfer Mode. A protocol that packs digital information into 53-byte cells (5-byte header and 48-byte payload) that are switched throughout a network over virtual circuits. Standardized by the ITU-T in 1988 to create a Broadband Integrated Services Digital Network (B-ISDN). Its ability to accommodate multiple types of media (voice, video, data) makes it a likely player for full service networks based on ADSL and VDSL.

ATM Forum. The organization tasked with developing and defining ATM standards. On the Internet, visit at http://www.atmforum.com for more info.

bandwidth. This is a reflection of the size or the capacity of a given transmission channel. In digital transmission, bandwidth is normally described in bits per second.

broadband. A type of transmission that shares the bandwidth of a medium--such as copper or fiber optic cable--to carry more than one signal. Broadband facilities have a bandwidth (capacity) greater than a voice grade line of 3 kHz. Such a broadband facility--typically coaxial cable--may carry numerous voice, video and data channels simultaneously. Each "channel" will take up a different frequency on the cable. "Guardbands" (empty spaces) exist between the channels to make sure that each channel does not interfere with its neighbor. A coaxial CATV cable is the "classic" broadband channel. Simultaneously it carries many TV channels. Broadband cables are used in some office LANs. But more common are the baseband variety, which have the capacity for one channel only. Everything on that cable to be transmitted or received must use that one channel. That one channel is very fast, so each device needs only to use that high speed channel for only a little of the time. (The problem is getting on the channel.) See also baseband.

central office (CO). A circuit switch that terminates all the local access lines in a particular geographic serving area; a physical building where the local switching equipment is found. xDSL lines running from a subscriber's home connect at their serving central office.

channel. A generic term for a communications path on a given medium; multiplexing techniques allow providers to put multiple channels over a single medium. See also multiplexer.

dedicated line. A transmission circuit that is reserved by the provider for the full-time use of the subscriber. Also called a "private line."

dial up. The process of initiating a switched connection through the network; when used as an adjective, this is a type of communication that is established by a switched-circuit connection.

digital subscriber line access multiplexer (DSLAM). The technical description of the Hitchhiker system. Also called "service access multiplexer." The DSLAM uses digital subscriber line (xDSL) and asynchronous transfer mode (ATM) technologies to deliver high speed data rates over the existing copper network. See also Hitchhiker, xDSL, and ATM. For an extensive description of the Hitchhiker system, refer to The Hitchhiker System manual from Diamond Lane Communications Corporation.

downstream/upstream

• downstream. In xDSL, the communications from the network towards the customer premises.
• upstream. In xDSL, the communications from the customer site up into the telecommunications network.
  
  More info on next page Telespeed Service