bri - Computer Definition
The user interface to an integrated services digital network (ISDN) intended for residential and small business applications. Also known as basic rate access (BRA) outside North America, BRI supports two bearer (B), or information-bearing, channels, each operating at the clear-channel rate of 64 kbps. Each B channel can support an independent data transmission, a PCMencoded voice conversation, or a number of statistically multiplexed subrate (low-speed) data transmissions. The B channels also can be aggregated, or bonded, to provide up to 128 kbps to a given conversation, such as a videoconference or Internet session. BRI also provides a data (D) channel at 16 kbps, which is intended primarily for purposes of signaling and control, messaging, and network management. The D channel also generally is made available for packet data transmission and low-speed telemetry when not in use for Modulated Carrier 0 1 0 0 1 1 1 0 Baseband Digital Signal signaling purposes. Also known as 2B+D, the combination of two B channels at 64 kbps each and the D channel at 16 kbps yields a three-channel configuration at a total signaling rate of 144 kbps over a conditioned, four-wire, twisted-pair local loop within 18,000 feet of the service central office (CO). A single BRI line can support up to 16 devices (e.g., telephones, facsimile machines, computers, and video cameras) that contend for access to the BRI channels through a terminal adapter (TA), also known as an ISDN modem. BRI also can support as many as 64 individual service profile identifiers (SPIDs), which are equivalent to directory numbers, one per terminal device. Many carriers offer BRI variations such as 0B+D and 1B+D targeted at specific applications such as credit card verification and telemetry, but all share the same BRI technology and the same signaling rate of 160 bps. The BRI interface between the CO and the customer premises is known as the U interface or Reference Point U, which runs at a signaling rate of 160 kbps, carrying two 64 kbps B channels, one 16 kbps D channel, and 16 kbps of overhead for framing, echo cancellation, and an embedded operations channel (EOC) for line testing and monitoring. In order to support this transmission rate in full duplex (FDX) mode over a physical two-wire, logical four-wire, twisted-pair local loop, the 2B1Q (2 Binary 1 Quaternary) encoding technique, with echo cancellation, is used in North America. In European and many other countries, the line coding technique employed is 4B3T (4 Binary 1 Ternary), a block code that combines four bits to represent one ternary signal state. See also 0B+D, 1B+D, 2B1Q, 4B3T, bonding, EOC, FDX, four wire, ISDN, local loop, Reference Point U, signaling and control, signaling rate, SPID, TA, and two-wire.