486 autonomous system
autonomous system. Collection of networks or areas under a common
administration sharing a common routing strategy.
availability. The amount of time a network is available to users, often expressed
as a percent uptime, or as a mean time between failure (MTBF) and mean time to
repair (MTTR). See also MTBF and MTTR.
available bit rate. See ABR.
B
backbone. A network that connects many other networks and acts as the
primary path for traffic between those networks.
backup links. Physical redundant connections between network devices.
backward explicit congestion notification. See BECN.
bandwidth. See capacity.
bandwidth domain. In a LAN, the set of devices that share and compete for
bandwidth. Bandwidth domains are bounded by switches, bridges, or routers. A
hub or repeater does not bound a bandwidth domain. Also called a collision
domain on Ethernet networks.
Banyan VINES. See VINES.
baseline. Characterization of the normal traffic flow and performance of a
network, used as input to a new or enhanced design for the network.
Basic Rate Interface. See BRI.
beacon. 1. Frame from a Token Ring or FDDI device indicating a serious
problem with the ring, such as a broken cable. 2. Frame sent by a wireless access
point during normal operation. Wireless clients listen to beacon frames to locate
access points.
BECN. backward explicit congestion notification. Bit set by a Frame Relay
network in frames traveling in the opposite direction of frames encountering a
congested path. Compare with FECN.
BER. bit error rate. Ratio of received bits that contain errors to the total number
of received bits.
Broadcast and Unknown Server 487
BERT. bit error rate tester. Device that determines the BER on a given
communications channel.
BGP. Border Gateway Protocol. Interdomain routing protocol that exchanges
reachability information with other BGP systems. BGP Version 4 (BGP4) is the
predominant interdomain routing protocol used on the Internet.
BIND. Berkeley Internet Name Domain. Implementation of DNS developed and
distributed by the University of California at Berkeley (United States).
bit error rate. See BER.
bit error rate tester. See BERT.
BOOTP. Bootstrap Protocol. Protocol used by a network node to determine the
IP address of its interfaces in order to achieve network booting.
Border Gateway Protocol. See BGP.
BPDU. bridge protocol data unit. Spanning Tree Protocol hello packet that is
sent out at configurable intervals to exchange information among bridges in a
network.
BRI. Basic Rate Interface. ISDN interface composed of two bearer (B) channels
for user data and one data (D) channel used for signaling. Compare with PRI.
bridge. Device that connects and passes frames between two network
segments. Bridges operate at the data link layer (Layer 2) of the OSI reference
model. A bridge filters, forwards, or floods an incoming frame based on the MAC
destination address of the frame.
bridge protocol data unit. See BPDU.
broadcast. Message that is sent to all nodes on a network. Compare with
multicast and unicast.
broadcast address. Special address reserved for sending a message to all
nodes. Generally, a broadcast address is a MAC destination address of all ones
(FF:FF:FF:FF:FF:FF in hexadecimal). Compare with multicast address and
unicast address.
Broadcast and Unknown Server. See BUS.

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