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Glossary

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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.

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.

border gateway

A router that facilitates communication with routers in

different autonomous systems.

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.

BRI

Basic Rate Interface: The ISDN interface that facilitates circuit-

switched communication between video, data, and voice; it is made up of
two B channels (64Kbps each) and one D channel (16Kbps). Compare with:
PRI. See also: BISDN.

bridge

A device for connecting two segments of a network and transmit-

ting packets between them. Both segments must use identical protocols to
communicate. Bridges function at the data link layer, Layer 2 of the OSI ref-
erence model. The purpose of a bridge is to filter, send, or flood any
incoming frame, based on the MAC address of that particular frame.

bridge ID

Used to find and elect the root bridge in a layer 2 switched inter-

network. The bridge ID is a combination of the bridge priority and base
MAC address.

bridging

A layer 2 process to block or forward frames based on MAC

layer addresses. Bridges are lower speed, lower port density switches.

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