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Glossary
61200051L1-1D ISU 2x64 Dual Port ISDN Service Unit User Manual 143
2B+D
The basic rate interface (BRI) in ISDN. A single ISDN circuit divided into two 64
kbps digital channels for voice or data and one 16 kbps channel for low speed data
(up to 9,600 baud) and signalling. 2B+D is carried on one or two pairs of wires de-
pending on the interface, the same wire pairs that today bring a single voice circuit
into your home or office. See ISDN.
U-interface
A twisted pair subscriber loop that connects the NT1 reference point to the ISDN
network, as defined in the I.411 Recommendation. This interface provides basic
rate access with an operating frequency of 160 kbps and an information rate of 144
kbps. Under U.S. regulations, this also marks the line of demarcation between cus-
tomer-owned equipment and the public network.
V.32
9.6 kbps, 2-wire duplex modem standard.
videoconferencing
The real-time, usually two-way, transmission of digitized video images between
two or more locations. Videoconferencing requires a wideband transmission facil-
ity. Transmitted images may be freeze-frame (where television screen is repainted
every few seconds to every 20 seconds) or full motion. Bandwidth requirements
for two-way video conferencing range from six MHz for analog, full-motion, full-
color, commercial grade TV to 56 kbps for digitally-encoded freeze-frame to 1.544
kbps for high-quality, full-color, full-motion TV.
X.25
A packet data transfer protocol for the B and D-channels. Defines the interface be-
tween data terminal equipment (DTE) and data circuit terminating equipment
(DCE) for terminals operating in the packet mode and connected to public data
networks by dedicated circuits.