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Glossary

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beacon

An FDDI device or Token Ring frame that

points to a serious problem with the ring, such as a
broken cable. The beacon frame carries the address of
the station thought to be down. See also: failure
domain.

BECN

Backward Explicit Congestion Notification:

BECN is the bit set by a Frame Relay network in
frames moving away from frames headed into a con-
gested path. A DTE that receives frames with the
BECN may ask higher-level protocols to take neces-
sary flow-control measures. Compare with: FECN.

BGP4

Border Gateway Protocol Version 4: Version

4 of the interdomain routing protocol most commonly
used on the Internet. BGP4 supports CIDR and uses
route-counting mechanisms to decrease the size of
routing tables. See also: CIDR.

binary

A two-character numbering method that uses

ones and zeros. The binary numbering system under-
lies all digital representation of information.

BIP

Bit Interleaved Parity: A method used in ATM to

monitor errors on a link, sending a check bit or word
in the link overhead for the previous block or frame.
This allows bit errors in transmissions to be found and
delivered as maintenance information.

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. Contrast with N-ISDN. See also: BRI, ISDN,
and PRI.

bit-oriented protocol

Regardless of frame content,

the class of Data-Link layer communication protocols
that transmits frames. Bit-oriented protocols, as com-
pared 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. Bootstrap mode then boots the
device with an operating system. The ROM can also
hold a small Cisco IOS.

bootstrap protocol

A protocol used to dynamically

assign IP address and gateway to requesting clients.

border gateway

A router that facilitates communi-

cation with routers in different autonomous systems.

boundary of dysfuntionality

The limit or scope of

the network problem. This boundary lies between
areas where the network is functioning properly and
where it ceases to function.

BPDU

Bridge Protocol Data Unit: A Spanning-Tree

Protocol initializing packet that is sent at definable
intervals for the purpose of exchanging information
among bridges in networks.

breakout boxes

These items are used to verify pin-

outs (e.g., TD--transmit data, RD--receive data,
CTS--clear to send) for all types of serial and parallel
connections.

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 transmitting packets between them. Both
segments must use identical protocols to communi-
cate. Bridges function at the Data-Link layer, Layer 2
of the OSI reference model. The purpose of a bridge is
to filter, send, or flood any incoming frame, based on
the MAC address of that particular frame.

broadband

A transmission methodology for multi-

plexing several independent signals onto one cable. In
telecommunications, broadband is classified as any
channel with bandwidth greater than 4kHz (typical
voice grade). In LAN terminology, it is classified as a
coaxial cable on which analog signaling is employed.
Also known as wideband. Contrast with: baseband.

broadcast

A data frame or packet that is transmit-

ted to every node on the local network segment (as
defined by the broadcast domain). Broadcasts are
known by their broadcast address, which is a destina-
tion network and host address with all the bits turned
on. Also called "local broadcast." Compare with:
directed broadcast.

broadcast domain

A group of devices receiving

broadcast frames initiating from any device within the
group. Because they do not forward broadcast frames,
broadcast domains are generally surrounded by routers.

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