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B
B Channel
B
Channel stands for "Bearer" Channel. B Channels are a fundamental
component of the ISDN architecture. A B channel operates at 64Kbps and can
be used for data, voice, facsimile, slow-scan video, and so on.
B-ISDN
B-ISDN stands for
Broadband ISDN. ISDN line rates come in two basic varieties, basic, primary
and broadband. Basic or "narrow" ISDN consists of two bearer (B)
channels and a data (D) channel. Each bearer channel can carry one PCM
voice conversation or data at a transmission rate of 64Kbps. The ISDN
Primary Rate Interface consists of 23 64Kbps channels for carrying voice,
data, and video and a data channel used for carrying signaling information.
It is similar to T1 signaling. B-ISDN (also called wide ISDN) has multiple
channels above the primary rate. In addition to the B and D channels there
are a number of additional channels defined. These include the A, C and H
series of channels.
B8ZS
B8ZS stands for
Binary 8 Zero Substitution. It is a technique that allows 64Kbps clear data
per T-carrier channel. Because of the ones density requirement of a
T-carrier system, a one must be inserted for every seven consecutive zeros.
B8ZS circumvents this requirement by inserting two code violations on the
physical link instead.
Backbone
The backbone of a
network is the portion of the network that carries the most significant
traffic. It is also the part of the network that connects many LANs or
subnetworks together to form a network. Bridges are often used to form
network backbones. In this configuration bridges often limit the local
traffic from the backbone to reduce congestion and isolate problems.
Backend System
A
backend system refers to the server portion of a client/server
relationship. In client/server computing the processing is done locally at
the user's machine (the client) and on a remote server. The computing that
is done at the client workstation is referred to as the front-end system
and the computing that is done at the server is referred to as the back-end
system.
Background Task
A
background task is a computer science term used to describe a computer
process that runs as a secondary job when multiple tasks are being
performed. It is also called "background processing." Task
priorities determine whether a task is the primary task or runs as a
secondary task. An example of a high priority data communications task
would be a task which handles data input from a communications link which
must be handled in a "real time" mode.
Background Spooling
A
background spooler is a software application that runs on a workstation as
a background process. When a user issues a print command, the background
spooler stores the document on the user's hard disk and then sends it to
the printer when the printer is available to print the document. Although
the workstation must remain connected to the network until the document is
processed, the user can continue to use the workstation for other tasks.
However, if the workstation is turned off or if its connection to the
network is broken, the print job will not be printed.
Backoff
Backoff is a term
most often used in the Ethernet LAN arena. A node attached to an Ethernet
LAN "backs off" when a collision occurs on the Ethernet bus. When
a collision does occur, a node will back off a random length of time before
it goes into a transmission mode again. The backoff algorithm is the
computer method for determining when this transmission retry will occur.
Backward Learning
Backward
learning is a process or algorithm that takes place in a network computer
used for routing packets or datagrams. As packets traverse a network and go
through servers, the server will learn routes based on the information
contained in the source and destination fields of the packets. The backward
routing algorithm is the algorithm used to determine future routes based on
this information.
Balun
Balun stands for
Balanced/Unbalanced. They are small devices that match the resistive
characteristics of two different types of media such as coaxial cable and
twisted pair wire.
Bandpass Filter
A
bandpass filter is an electronic circuit designed to allow a single band of
frequencies to pass. It is used to receive a certain frequency or range of
frequencies and "filter out" unwanted frequencies.
Bandwidth
Bandwidth is the
difference between the highest and lowest frequencies that can be
transmitted across a transmission line or through a network. It is measured
in Hertz (Hz) for analog networks and bits per second (bps) for digital
networks.
Banyan Vines
Banyan
Systems, Inc., founded in 1983, is one of the unsung heroes among LAN
vendors, offering a broad range of products that provide sophisticated
services in wide area network environments. Banyan built its network
operating system, VINES (Virtual Networking System), as a layer on top of
UNIX in order to take advantage of the operating system's multi-user,
multitasking capabilities. But the company made this technological leap
before most large companies believed in the viability of UNIX as an
enterprise-level operating system.
Barrel Connector
A
barrel connector is a barrel shaped connector that join two 10Base5
(thicknet) pieces of Ethernet coax together.
Base 16
The
hexidecimal number system is a base 16 numbering system. It is the numbering
system used to condense binary bytes into a compact form for printing or
analysis of computer data. It is composed of the numbers 0-9 and the
letters A-F. Each "nibble" (four bits) of a byte can be
represented by one of the 16 characters.
Baseband
Baseband is a
form of modulation where signals are placed directly on the transmission
media in their original form, i.e., no frequency division multiplexing is
performed. A baseband modem is a modem that does not modulate the signal
before transmission, thereby transmitting the signal in its native form.
Baseband signaling is the transmission of either digital or analog signals
at their original frequencies.
Basic Input/Output System (BIOS)
The Basic Input/Output System is a computer storage area
(buffer) which stores data to be sent to a computer's hardware components
such as a serial interface adapter.
Basic Rate Interface
BRI is
the Basic Rate Interface in ISDN. It is also referred to as 2B+D. In ISDN's
BRI interface, 2B stands for two bearer channels, D stands for a data
channel. A BRI ISDN circuit is composed of two 64Kbps bearer channels which
may be used for voice or data, and one 16Kbps data channel. The data
channel is also used for signaling.
Batch Processing
There
are two different types of processing, one is called real time or
interactive processing and the second is called batch processing. Batch
processing is also referred to as batch mode processing, off-line
processing, batch file processing and deferred time processing.
Batch
processing refers to the processing mode where many jobs are combined
together and run serially to complete one specific task. While these jobs
are running, typically nothing else on the computer can run. A batch file
is executed which contains a list of tasks to be completed for the batch
process. JTM (Job Transfer and Management) and RJE (Remote Job Entry) are
forms of batch processing.
Baud Rate
Baud
rate is synonymous with the signaling rate. Baud rate and Bit rate or Bits
per Second (bps) are often confused. The strict definition of baud rate
refers to the number of times per second the signal on the communication
link changes. In other words, if a modem is able to shift between
frequencies 9600 times per second, then the baud rate is 9600. If one bit is
represented by each frequency shift then the baud rate and bit rate would
be the same, 9600. However if each frequency shift represented two bits,
then the baud rate would be 9600 and the bit rate would be 9600 X 2 =
19,200bps.
BCD
BCD (binary coded
decimal) is a numbering system where binary numbers (1s and 0s) represent
decimal numbers 0-9. It takes four binary numbers to represent a decimal
number. For instance, the number 1 is represented as 0001. The number 2 is
represented as 0010. The number 3 is represented as 0011 and so on.
Beacon
A beacon is a
type of Token Ring frame that is used to indicate a catastrophic condition
on the physical ring. Conditions such as broken ring cables or
malfunctioning workstations or MAUs (Multistation Access Unit) will create
this condition. Beaconing refers to the recovery process that takes place
when this type of catastrophic situation exists.
Bearer Channel
A
Bearer Channel, or B Channel, is a fundamental component of the ISDN
architecture. A B channel operates at 64Kbps and can be used for data,
voice, facsimile, slow-scan video, and so on.
BECN
BECN stands for
Backward Explicit Congestion Notification. It is a term used to describe a
condition found in a Frame Relay network. The BECN bit is set in a Frame Relay
frame to indicate that congestion may be experienced by traffic sent in the
opposite direction.
BER
BER stands for
Basic Encoding Rules. Standard rules for encoding data units described in
ASN.1. Sometimes incorrectly lumped under the term ASN.1, which properly
refers only to the abstract syntax description language, not the encoding
technique.
BER
also stands for Bit Error Rate. Bit Error Rate is the ratio of bit errors
received in relation to the total number of bits transmitted. It is derived
by dividing the errored bits by the number of bits transmitted (BER =
Errored Bits/Bits Transmitted). BER is measured over a finite period of
time. When bit error rates are extremely high, channel efficiency decreases
due to the need to retransmit errored data.
BERT
A BERT is a Bit
Error Rate Tester. It is a test tool that measures BER.
Best Path
Best
path is a term used to describe the best path taken by a packet or datagram
when traversing a network. The best path is the optimal path between source
and destination nodes. It is determined via routing protocols that operate
at the network layer of the OSI protocol stack. RIP (Routing Information
Protocol) is an example of a protocol that supports performance route
optimization.
BGMP
The Border Gateway Multicast Protocol (BGMP) maintains a
group-prefix state in response to messages from BGMP peers and
notifications from M-IGP components. Group-shared trees are rooted at the
domain advertising the group prefixes covering those groups. When a
receiver joins a specific group address, the border router towards the root
domain generates a group-specific Join message, which is then forwarded
Border-Router-by-Border-Router towards the root domain. BGMP Join and Prune
messages are sent over TCP connections between BGMP peers, and the BGMP
protocol state is refreshed by KEEP ALIVE messages periodically sent over
TCP.
BGMP routers build group-specific bidirectional forwarding state as they
process the BGMP Join messages. Bidirectional forwarding state means that
packets received from any target are forwarded to all other targets in the
target list without any RPF checks. No group-specific state or traffic
exists in parts of the network where there are no members of that group
BGP-4
The Border Gateway Protocol (BGP) is an inter-Autonomous
System routing protocol. The primary function of a BGP speaking system is
to exchange network reachability information with other BGP systems. BGP-4
provides a new set of mechanisms for supporting classes interdomain
routing.
Binary
Binary is the
numbering system used by computers to represent information. Binary numbers
consist of numbers represented by two values, 1s and 0s. Most computers
store information in bytes (and multiples of bytes) that consists of 8
bits. These 8 bits can be combined to form 256 different values. The values
represented by these 8 bits would be between 0 and 255. 0 would be
represented by 00000000, decimal 1 by 00000001, decimal 2 by 00000010,
decimal 3 by 00000011, decimal 4 by 00000100 and so forth until 255 which
is represented by 11111111.
Binary 8 Zero Substitution
Binary
8 Zero Substitution (B8ZS) is a technique that allows 64Kbps clear data per
T-carrier channel. Because of the ones density requirement of a T-carrier
system, a one must be inserted for every seven consecutive zeros. B8ZS
circumvents this requirement by inserting two code violations on the
physical link instead.
Binary Coded Decimal
A
numbering system where binary numbers (1s and 0s) represent decimal numbers
0-9. It takes four binary numbers to represent on decimal number. For
instance, the number 1 is represented as 0001. The number 2 is represented
as 0010. The number 3 is represented as 0011 and so on.
Binary Transfer
A binary
transfer is a transfer of data between two computers where the contents of
the data stream are not altered during transmission. The data
communications facilities (such as modems) do not evaluate or manipulate
the data as it is being transferred. The binary information is sometimes
referred to as "raw data." For example, when using the FTP
protocol the binary option is used so that the data will remain in its
original state after the transfer of data has taken place.
Bindery
A bindery is a
Novell NetWare (version 3.x) database that contains definitions for users,
groups and workgroups. It contains three components: objects, properties
and property data sets. Objects include both logical and physical entities
such as users, servers, printers and so forth. Properties are
characteristics of each object and contain information such as addresses,
rights and passwords. Property data sets are the values assigned to the
properties.
BIOS
BIOS stands for
basic Input/Output system. The BIOS is a computer storage area (buffer)
which stores data to be sent to a computer's hardware components such as a
serial interface adapter.
Bis
Bis, as seen
following some of the ITU-T standards, is French for second. Therefore a
standard such as V.22 bis means that it is the second V.22 standard
defined. Ter is French for third and is also found after standards when it
is the third time the standard has been defined.
Bisync
Bisync is short
for bisynchronous transmission. Bisynchronous transmission is a synchronous
character oriented protocol developed by IBM in 1964. It is still in wide
use today, even though the newer bit oriented protocols used today are much
more efficient.
Bit Interleaving
Bit
interleaving refers to the process of interleaving bits within a serial communications
link. Lower speed transmission links are time division multiplexed onto a
higher speed communications link by interleaving bits from each channel
onto the high-speed link. It must be noted that depending on the
technology, bits or bytes may be interleaved.
Bit Rate
The
bit rate is the number of bits transmitted per second (bps). For instance,
commonly used rates for modem speeds are 300bps, 1200bps, 9600bps,
14,400bps, and 19,200bps. Another way of writing 19,200bps is 19.2Kbps.
Kbps stands for kilobits per second which would mean 1000 bits transmitted
per second times 19.2. 1.544Mbps is the T1 rate and is 1,544,000bps.
Bit Stuffing
Bit
stuffing allows binary data to be transmitted on a synchronous transmission
line. Within each frame are special bit sequences that identify addresses,
flags, and so forth. If the information (data) portion of the frame also
contains one of these special sequences, a zero is inserted by the
transmitting station and removed by the receiving station.
The
reason for this becomes clear when you consider the example of a flag. In
bit oriented protocols, flags are used to signal the start and end of a
frame. The receiver monitors the incoming data looking for the flag to
identify the frame. If the data portion of the frame contained the same
sequence of bits as the flag, the receiving node would incorrectly identify
the ending flag.
Black Box
A
black box is a communications device (or any device for that matter) whose
contents are unknown. The input to the box may be known as well as the
output of the box, however how it performs its function is not known. The
term black box testing is a related term. Black box testing is testing of a
product without knowing the contents of the system under test.
Block Error Rate
Block
error rate is the ratio of the number of blocks received that contain at
least one bit error to the total number of blocks of data received. (BLER =
Blocks with Error/Blocks Transmitted). Blocks are frames are typically
considered synonymous. The size of the block is determined by the data link
protocol, i.e., an Ethernet frame is 1500 bytes or less of data, Token Ring
frames are typically 2k or 8k bytes in length.
BNC
BNC connectors
are small devices used for Thin Ethernet connections and terminations
(10Base2). There are several different types of BNC connectors depending on
their function. A BNC Barrel Connector joins two thin Ethernet cables
together. A BNC terminator is used to terminate the end of an Ethernet
cable. It acts as a resistive load that absorbs the signal (frame) at each
end of an Ethernet LAN. BNC adapters allow you to connect different types
of Ethernet cable together, such as Thinnet to Thicknet.
Break Out Box
A break
out box is a hand held device that allows a tester to monitor and
manipulate the individual leads of an interface cable such as RS232. LEDs
typically found on a breakout box indicate whether the individual lead is
in a high or low
state.
BRI
BRI is the Basic
Rate Interface in ISDN. It is also referred to as 2B+D. In ISDN's BRI
interface, 2B stands for two bearer channels, D stands for a data channel.
A BRI ISDN circuit is composed of two 64Kbps bearer channels which may be
used for voice or data, and one 16Kbps data channel. The data channel is
also used for signaling.
Bridge
A bridge is a
hardware device that connects LANs together. It can be used to connect LANs
of the same type, such as two Token Ring segments or LANs with different
types of media such as Ethernet and Token Ring. It operates at the Data
Link Layer of the OSI reference model.
Broadband
Two methods are
used to transmit signals between nodes: baseband and broadband. In the
context of LANs, broadband refers to analog transmission of digital
signals, and baseband refers to digital transmission of digital signals.
Broadcast
The term
broadcast is used to indicate sending information over a network to more
than one device simultaneously. Several broadcast terms are used in the
data communications industry.
Broadcast Channels
Broadcast
channels are, as the name implies, similar to short-wave radio
conversations. A node broadcasts on the common channel, and all other nodes
connected to the channel listen to the message. The channel might consist
of electromagnetic emissions (that is, radio), or a wire or cable to which
all nodes are attached (such as Ethernet). As with users of CB radio
channels, more than one node might begin to transmit at the same time. When
that happens, each garbles the other's message. They all must stop and then
start over again in such a way that subsequent collisions are not likely to
happen. Alternatively, transmissions can be scheduled so that more than one
transmission never takes place at the same time.
Broadcast Message
Broadcast
messages are messages that are sent simultaneously to all users on a given
network. A broadcast list is a list of specific users on a network that
will receive the information. All other users on the network will not
receive the message.
Broadcast Storms
Due to
differences between nodes and bridges in different parts of the network, a
broadcast frame can sometimes be misinterpreted. This leads to another
broadcast frame by the bridge which misinterprets it, the second broadcast
frame is again misinterpreted, and so on. The result is a "storm"
of broadcast frames that can severely impact network performance. Sometimes
storms can persist and eventually bring down the entire network. Such
problems can be very difficult to resolve.
Brouter
Also written as
b/router, this is a node that performs the functions of both a bridge and a
router, for example, bridging frames between two subnets but routing
packets from either subnet to another network.
Burst
The term burst,
or burst transmission, is used in data communications to mean a large
amount of data transmitted over a very short time. Bursty traffic or bursty
data implies a lot of data transmitted at random intervals.
Bus
There are many
types of buses. There are internal buses, rxternal buses, and LANs that
operate on bus topologies. Internal buses are buses within a PC which
connect the central processor with the video controller, disk controller
hard drives and memory. External buses are buses such as AT, ISA, EISA, PCI
and MCA that are internal to a PC but not "local buses." Network
buses refer to the type of topology that is used when connecting nodes in a
local area network environment. A network with a bus topology has a single
wire or cable with multiple taps; the ends of the bus are unconnected.
Byte Per Second
Bytes
per second or characters per second is a term typically used to describe
the number of characters that can be printed by a printer per second on a piece
of paper. BPS normally refers to bits per second.
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