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- BABT
(British Approvals Board for Telecommunications) An independent organization that tests
telecommunications equipment. Its processes are known for their
rigorousness and labyrinthine complexity.
- Back end The server
part of a client/server application. It provides services across
the network that have been requested by the client. For example,
a back end may be a database server that responds to SQL requests
from a workstation running a front end application.
- Back-up server Software
or hardware which copies files so that there are always two current
copies of each file. Also known as a shadow server.
- Backbone A high-capacity
network that links together other networks of lower capacity.
A local backbone network would typical y be an FDDI network acting
as an in building backbone to link together multiple LANs. A wide
area backbone network would typically use digital leased circuits
and multiplexers or routers.
- Background Task or Mode A
secondary function perforated by a computer without interrupting
its current or primary task.
- Back-up domain controller A
server in a network domain that keeps and uses a copy of the domain's
user accounts database to validate logon requests.
- Balun A transformer
that levels out impedance differences so that a signal generated
on to a coaxial cable can transfer on to twisted pa r. Baluns
are often used so that IBM 3270 terminals can run off twisted
pair, or to allow co-axial Ethernet to be operated over UTP.
- Bandwidth The range
of frequencies a transmission line or channel can carry: the greater
the bandwidth, the greater the information - carrying capacity
of a channel. For a digital channel this is defined in bit/s.
For an analog channel it is dependent on the type and method of
modulation used to encode the data.
- 10Base2 A form of
Ethernet and IEEE 802.3 network cabling using thin coaxial. It
refers to I0Mbit/s speed Baseband transmission over 200 meters
maximum length in practice 185m) and is commonly known as Cheapernet.
- 10Base5 A form of
Ethernet and IEEE 802.3 network cabling using thick coax. It refers
to 10Mbit/s speed Baseband transmission and 500m maximum length.
- 10BaseT A form of
Ethernet and I EEE 802.3 network cabling using twisted pair cabling.
It refers to 10Mbit/s speed Baseband transmission twisted pair
cable with a maximum segment length of 100m.
- 100BaseT IEEE standard
from proposals by the Fast Ethernet Alliance (including 3Com and SynOptics). It will support Category 3,4 & 5 UTP cabling.
- 100BaseVG-AnyLan A
competing proposal to 100BaseT (promoted by Hewlett Packard, IBM
and Proteon among others) to the IEEE for a 100Mbit/s standard
over voice grade UTP the cable most users already have installed
in existing 10BaseT systems. Based on Quartet Signaling and demand
priority protocol, it preserves the infrastructure and will need
only a new hub and upgraded adapters in PCs/work stations. It
claims support for Category 3,4 & 5 UTP cabling for both Ethernet
and Token Ring.
- Baseband A term defining
any network in which the information is modulated onto a single
carrier frequency. The digital input is applied directly to the
transmission media without the intervention of a modulating device,
which works well if there is wide bandwidth and distances no more
than several hundred meters are involved. It is common in LANs
and limited distance modems. All stations attached to the network
have to participate in every transmission. Simpler and cheaper
than Broadband, it permits only one "conversation" at
a time as the whole of the bandwidth is used to transmit a single
digital signal. Ethernet is a baseband network.
- Base station A fixed
radio transmitter/receiver which electronically relays signals
to and from mobile voice and data terminals or handsets.
- Basic Rate Access Two
641Kbit/s "B" channels + one 16Kbit/s "D"
channel (2B + D), carrying user traffic and signaling information
respectively to the user via twisted pair local loop.
- Baud A unit of s gnarling
speed, expressed in terms of the number of discrete conditions
or signal events per second. It is on y the same as bit/s, when
one discrete signaling condition is used to transmit a single
bit of data.
- Beaconing Token Ring
process to recover the network when any attached station has sensed
that the ring is inoperable because of a hard error Stations can
withdraw from the ring if needed. A station detecting a ring failure
upstream transmits (beacons) a special MAC frame used to isolate
the location of the error using beacon transmit and beacon repeat
modes.
- Bindery A database
that contains definitions for entities such as users, groups and
workgroups in the Novel NetWare LAN network operating system environment.
The bindery supports the design, organization and secure operation
of the NetWare environment.
- Bipolar transmission Method
of sending binary data in which negative and positive states alternate.
Used in digital transmission facilities.
- B-ISDN (Broadband ISDN) The
proposed advanced version of ISDN, providing speeds of 155.52Mbit/s
and higher. Standards and switching technology that will work
this fast are under development. It promises universal coverage
based on ATM/SDH technologies and optical fiber, supporting data,
voice and video traffic.
- Bit A binary unit
of information that can have two values, 0 or, 1. The word comes
from a contraction of binary digit.
- Bit Error Rate The
percentage of received bits on a digital link that are in error
relative to the number of bits received, usually expressed to
a power of I 0
- Bit Error Rate Tester A
device for testing the reliability of a digital datacommunications
link. The BERT generates specific data patterns that are routed
through a communications device for comparison at the receiving
end. The errors are counted by the BERT.
- Bit Interleaving A
form of Time Division Multiplexing (TDM) for synchronous protocols,
including HDLC, SDLC, BiSync and X.25 Bit inter-leaving retains
the sequence and number of bits, so that correct synchronization
is achieved between both ends.
- Bits per second The
rate at which individual bits are transmitted across a communications
link or circuit; written bit/s. One thousand bit/s is 1 Kbit/s,
and one mil ion bit/s is 1 Mbit/s.
- Block A group of characters
or bytes treated as a unit.
- BNC connector A cylindrical
push-and-twist connector for connecting thin co-axial cable, such
as 10Base2 "thin wire" Ethernet, and to link thin wire
Ethernet to network interface cards, transceivers and other network
elements. Said to be short for Bayonet Neill-Concelman after the
developers of the connector. Also referred to as a Barrel Nut
Connector.
- Booting Loading a
computer memory with information needed for it to operate. Remote
booting refers to loading software over the network.
- Boundary Routing A
3Com proprietary name for a method of accessing remote networked
locations, such as a bank branch office. Effectively a form of
bridging, the idea is to reduce the need for technical expertise
locally and the cost of equipment at the remote site and manage
the communications from head office.
- BRA (Basic Rate Access) BRA
provides ISDN users with access to two 64Kbit/s data channels,
It is defined in ITU-TS Recommendation I.420 which covers a 2B
+ D-channel where the B channel is a 64Kbit/s channel, and the
D-channel is a 16Kbit/s signaling channel.
- Bridge Device connecting
two separate networks at the OSI Data Link Layer (Level Two Media
Access Control Layer). Once bridging is accomplished, the bridge
makes interconnected LANs look like a single LAN, passing data
between the networks and filtering local traffic. There are two
key classifications of bridge: those supporting Spanning Tree
and, for Token Ring networks, those supporting Source Routing.
Bridges connect networks using dissimilar protocols and do not
interpret the data they carry. They control network traffic and
security, filtering where necessary to boost network, performance
and contain sensitive data to particular LAN areas.
- BS5750 A British Standards
Institute standard with certification procedures that says an
organization is in control of its quality procedures, at least
in terms of consistency. Now identical to IS09000.
- BSC, BiSync
(Binary Synchronous Communications) Rules developed by IBM for the synchronous
transmission of binary coded data as a serial stream of binary
digits. Synchronization is achieved by using control characters
recognizable as bit patterns which do not appear within the body
of the message.
- BSGL (Branch Systems General License)
A
license which must be obtained by any organization seeking to
link its own private network to the Public Switched Telephone
Network (PSTN). A separate license must be held for each individual
site.
- BSI (British Standards Institute) The
UK standards body responsible for input into European and international
standards setting bodies like ISO and the ITU-TS.
- Broadband Also referred
to as wideband. A term describing any network that multiplexes
multiple, independent network carrier frequencies on to a single
cable. It allows multiple simultaneous "conversations",
since the independent networks operate on different frequencies
and do not interfere with each other. In LAN terminology, it refers
to a system in which multiple channels access a medium, for example
co-axial cable, that has a large bandwidth using Radio Frequency (RF) modems. This may allow the co-axial cable to carry multiple
separate LANs whose transmission is being modulated at different
frequencies. In cable television (CATV), broadband describes the
ability to carry 30 or more TV channels and is synonymous with
wideband.
- Broadcast The simultaneous
transmission of data via a network from one terminal to a set
of destinations or to all destinations.
- Brouter An industry
term for a device with the functionality of a bridge and router.
It supports more than two LAN connections and uses Level Two addresses
for routing. The term is mostly used by bridge vendors.
- Buffer A temporary
storage place for data, designed to compensate for a difference
In transmission speeds or to hold data when there is a difference
in timing of events. It can be a software program, a storage facility
or a hardware device, ensuring the data always has somewhere to
go, even if it has to be held up for while in the buffer until
it can be transmitted to the destination.
- Bus topology A type
of network in which all tie devices are connected in a line to
a single cable. A bus network has two distinct ends. All devices
which attached to a bus network have equal access to it and they
can see all the messages that are put on to the network. Each
device determines which messages are intended for it alone, and
selects those.
- Byte Eight bits forming a unit of data. Usually each
byte stores one character.
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