gloss_B

B

backbone.

A backbone is the main "spine" or segment of a building or campus network. Departmental networks are attached as "ribs" to the central backbone. The long-haul intercity segments of public carrier networks are also referred to as backbones.

bandwidth on demand.

A concept in wide area networking that allows a user or application to agglomerate additional WAN bandwidth as the application warrants . It enables users to pay only for bandwidth that they use, when they use it. Implementing bandwidth on demand requires switched services, such as ISDN or Switched 56 lines.

bandwidth.

Bandwidth is the difference between the highest and lowest frequency a channel can conduct, measured in Hz. The bandwidth of a voice-grade telephone line is about 4KHz, while the bandwidth of a broadcast TV channel is 6MHz. The term bandwidth is often used informally to refer to a channel's throughput, which is typically measured in Kbits/sec or Mbits/sec. All other things being equal, a channel with twice the bandwidth of another channel can carry twice as much trafficthat is, it can have twice the throughput. See throughput.

Basic Rate Interface (BRI).

BRI is an ISDN service that offers two "bearer" (B) channels with 64Kbits/sec throughput that can be used for bulk data transfer plus a "data link" (D) 16Kbits/sec channel for control and signaling information.

blackout .

A blackout or power outage is an interruption or total loss of commercial electrical power. Uninterruptible power supplies provide battery- backed up power that will supply electricity during a blackout (while their batteries last).

bridge.

A bridge connects two networks of the same access method, for example, Ethernet to Ethernet or Token Ring to Token Ring. A bridge works at the OSI's Media Access Control layer, and is transparent to upper-layer devices and protocols. Bridges operate by filtering or forwarding packets according to their destination addresses. Most bridges automatically learn where these addresses are located, and thus are called learning bridges.

Broadband ISDN (B-ISDN).

A class of emerging high speed data and voice services for the wide-area network. Switched Multimegabit Data Services and Asynchronous Transfer Mode are two emerging B-ISDN services that were designed to provide megabits and gigabits of bandwidth across a wide area network.

broadcast storm .

In a broadcast storm, network congestion occurs when excessive numbers of frames are broadcast.

broadcast.

A broadcast message is addressed to all stations on a network.

brouter.

A brouter is a device that can transparently bridge protocols as well as route them. It is a hybrid of a bridge and a router.

brownout.

A brownout is an abnormally low voltage on commercial power distribution lines. Power utilities may intentionally produce a brownout when there is near overload demand for power, or natural conditions, such as storms, fires, or accidents, may cause a brownout.

bus topology.

A bus topology is a network architecture in which all of the nodes are connected to a single linear cable.