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Glossary

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BISDN

Broadband ISDN: ITU-T standards created to manage high-

bandwidth technologies such as video. BISDN presently employs ATM
technology along SONET-based transmission circuits, supplying data rates
between 155Mbps and 622Mbps and beyond. See also: BRI, ISDN, and PRI.

bit

One digit; either a one or a zero. Eight bits make a byte.

bit-oriented protocol

Regardless of frame content, the class of Data Link

layer communication protocols that transmits frames. Bit-oriented proto-
cols, as compared with byte-oriented, supply more efficient and trustworthy
full-duplex operation. Compare with: byte-oriented protocol.

block size

Number of hosts that can be used in a subnet. Block sizes

typically can be used in increments of 4, 8, 16, 32, 64, and 128.

Boot ROM

Used in routers to put the router into bootstrap mode. Boot-

strap mode then boots the device with an operating system. The ROM can
also hold a small Cisco IOS.

boot sequence

Defines how a router boots. The configuration register

tells the router where to boot the IOS from as well as the configuration.

bootstrap protocol

A protocol used to dynamically assign IP addresses

and gateways to requesting clients.

border gateway

A router that facilitates communication with routers in

different autonomous systems.

border peer

The device in charge of a peer group; it exists at the edge of

a hierarchical design. When any member of the peer group wants to locate a
resource, it sends a single explorer to the border peer. The border peer then
forwards this request on behalf of the requesting router, thus eliminating
duplicate traffic.

border router

Typically defined within Open Shortest Path First (OSPF)

as a router that connected an area to the backbone area. However, a border
router can be a router that connects a company to the Internet as well. See
also: OSPF.

BPDU

Bridge Protocol Data Unit: A Spanning Tree Protocol initializing

packet that is sent at definable intervals for the purpose of exchanging infor-
mation among bridges in networks.

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