BACKBONE
The main segment of a network to which all other segments are connected. It links several workgroup LANs together in a single building, or several networks together in a campus environment. All systems with connectivity to the backbone have connectivity to one another, but systems can set up private connections that bypass the backbone for reasons of cost, performance, or security. 
Example of a Token-Ring backbone.
Three floors - TR LAN - federated by two backbones.
Backbones could be equipped with high speed bandwidth network such as ATM.
The enterprises servers could be installed on both backbones.
In the following case, the backbone can be used as well to load-balanced the traffic on the network.

BACKOFF ERROR

BACP
Bandwidth Allocation Control Protocol

BALUN
Balanced Unbalanced

BAN
Boundary Access Node 
An IBM ¨ enhancement that refers to the RFC 1490 specification for bridged SNA over frame relay. BAN carries the source and destination MAC addresses in the network packets. 

BANDWIDTH
The bandwidth of a transmitted communications signal is a measure of the range of frequencies the signal occupies. The term is also used in reference to the frequency-response characteristics of a communications receiving system. All transmitted signals, whether analog or digital have a certain bandwidth. 
The difference between the highest and lowest frequencies available for network signals. The rated throughput capacity of a given network medium or protocol.
The number of bits of information that can move through a communications medium in a given amount of time; the capacity of a telecommunications circuit/network to carry voice, data, and video information. Typically measured in Kbps and Mbps. Bandwidth from public networks is typically available to business and residential end-users in increments from 56Kbps to T-3. 

BAOC
Barring of All Outgoing Calls - prevent a user to send call on a GSM network

BAP
Bandwidth Allocation Protocol

BASEBAND
A communication method where digital signals are pulsed directly on the transmission medium without change in modulation. In baseband LANs, the entire bandwidth of the cable is used to transmit a single signal and only one signal can be transmitted at a time.
Characteristic of a network technology where only one carrier frequency is used. Baseband can be contrasted with broadband, where multiple carrier frequencies are used. Ethernet is an example of a baseband network.

BASE64
The base 64 encoding system encodes 3 bytes in 4 for each byte which contains 6 significant bits.This program allows the conversion to find out the original file.

BAUD
Jean-Maurice-Emile Baudot
French engineer Jean-Maurice-Emile Baudot.
Initially used to measure the transmission speed of telegraph, the baud rate is used today to 
measure a data transmission speed with a modem.
The number of voltage or frequency transitions per second. 
At low speeds only, baud may be equal to bits per second

BBN
Bolt Beranek and Newman ¨

BBS
Bulletin Board System

Bchannel
Bearer Channel - ISDN 
Part of an ISDN full duplex interface able to carry voice or data over an ISDN network at 64 Kb/s 

BCP
Bridging Control Protocol

BCU
Bus-Control Unit

BCVT
Basic Class Virtual Terminal - OSI

BDC
Backup Domain Controller - Windows NT. Server which authenticates users and is promoted as a Primary Domain Controller in case of failure of the server which acts as the controller. Microsoft ¨

BDCS
Broadband Digital Cross-Connect System - SONET

BEACONING
A signal from an IBM Token-Ring device indicating a serious problem with the ring, such as a broken cable. Beacon frames contain the address of the assumed down station.
AUTOMATIC RECOVERY ATTEMPT THROUGH THE BEACON PROCESS
Beaconing is the process of isolating a a fault domain so that recovery actions can take place. The fault domain consists of:

1. The station reporting the failure (the beaconing station)
2. The station upstream from the beaconing station
3. The ring medium between them

When the ring is beaconing it alerts all stations on the ring that the token protocol has been suspended. Through ring poll / neighbor notification each station knows the address of its upstream neighbor. This allows the identification of the elements of the failure domain.

The beacon process consists of transmitting Beacon MAC frames every 20 ms without needing a token. The beaconing station derives its time base from its own internal crystal oscillator and not from the clock recovered from its receiver port. 
Upon receipt of a Beacon MAC frame a station will enter either the Beacon Repeat mode or the Beacon Transmit mode (as will be discussed). A station which is in the Insertion Process will terminate its Open command with an error and will remove itself from the ring.

There are four types of Beacon MAC frames that might be seen:

A SET RECOVERY MODE (Priority 1, the highest priority) is never originated by the adapter itself. It is reserved for a recovery process implemented in the attached product. Don't expect to ever see a Priority 1 beacon. If you do, find out who sent it, and why.

A SIGNAL LOSS (Priority 2) beacon is transmitted when a Monitor Contention timeout occurs and the Contention Transmit mode was entered because of a signal loss condition being detected.

A STREAMING SIGNAL, NOT CLAIM TOKEN (Priority 3) beacon is transmitted when a Monitor Contention timeout occurs and no Claim Token MAC frames were received during the contention period. Notice that this implies that a differential Manchester clock (idle clock) was received. Otherwise a Priority 2 beacon would have resulted.

A STREAMING SIGNAL, CLAIM TOKEN (Priority 4) beacon is transmitted when a Monitor Contention timeout occurs and one or more Claim Token MAC frames were received during the contention period.

BECN
Backward Explicit Congestion Notification 
A bit set by a frame relay network that notify an interface device - DTE - that congestion avoidance procedures should be initiated by the sending device. 
Bits within a frame relay header to indicate congestion in the path in the opposite direction as the frame is flowing. 

BER
Basic Encoding Rule

BER
Bit Error Rate - The number of erroneous bits in a data transmission.

BERT
Bit Error Rate Test - A common test for WAN lines.

BES
Best Effort Service - IETF

BG
Border Gateway - gateway node which allows the connection of GPRS networks

BGP
Border Gateway Protocol 
An interdomain routing protocol that is a potential replacement for EGP - Exterior Gateway Protocol - BGP is defined by the RFC 1105, which was jointly authored by Cisco ¨ and IBM ¨.

A protocol in the IP suite designed to exchange network reach ability information with other BGP systems in other autonomous systems. BGP speakers provide routing updates including a network number, a list of autonomous systems that the routing information has passed through, and a list of other path attributes. BGP4 replaces the original BGP3.

BIC-Roam
Barring of Incoming Calls when roaming outside the home PLMN. Prevent the user to receive the calls when outside its PLMN.

BICI
Broadband Inter - Carrier Interface

BIGA
Bus Interface Gate Array - Cisco ¨ 

BIOD
Block Input / Output Daemon

BIOS
Basic Input / Output System

BIP
Bit Interleaved Parity - ATM

BIR
Burst Information Rate 
The Burst Information Rate - BIR - is the speed or rate of information that the customer may need over and above the CIR. A burst is typically a short duration transmission that can relieve momentary congestion in the LAN or provide additional throughput for interactive data applications

B-ISDN
Broadband Integrated Services Digital Network A high-speed communications standard for WAN's for high-bandwidth applications - video, voice, and graphics.

BIT
Binary Digit 
The smallest unit of information handled by a computer. One bit expresses a 1 or a 0.

BIU
Bus Interface Unit

BLSR
Bidirectional Line Switch Ring - SONET

Bluetooth
A global initiative by Ericsson, IBM, Intel, Nokia and Toshiba to set a standard for cable-free connectivity between mobile phones, mobile PCs, handheld computers and other peripherals. It will use short-range radio links in the 2.45 GHz Instrumentation Scientific and Medical ISM - " free band ". The term Bluetooth comes from a Scandinavian king who first federates the Scandinavian countries. The king had a dark broken tooth.

BML
Business Management Layer - Used for the SLA for the optical layer clients. 

BMP
BitMap - File System

BMT
Bean Managed Transactions 
The developer of the component takes in charge the management process.

BNC
Bayonet Neil Concelman Connector / Barrel Nut Connector
A connector for coaxial cables that locks when one connector is inserted in another and rotated 90 degrees.

BNI
Broadband Network Interface

BNM
Broadband Network Module

BNN
Boundary Network Node 
An IBM router enhancement that refers to the RFC 1490 specification for routed SNA over frame relay. BNN allows native SNA traffic to communicate over public or private frame relay networks directly with an SNA processor. BNN does not carry the source and destination MAC addresses in the network packet.

BOIC
Barring of Outgoing International Calls. Additional service which prevents international calls.

BOOTP
Bootstrap Protocol - RFC 951

BOP
Bit Oriented Protocol

BPDU
Bridge Protocol Data Unit - Bridge Spanning Tree Protocol. A data unit containing information passed between connected stations regarding connection status. 

BPS
Bit Per Second

BPSK
Binary Phase-Shift Key

BPV
Bipolar Violation. T1 line code/signal errors. 

BRI
Basic Rate Interface - ISDN
ISDN Interface composed of two 64 KB / B-channels for data and one 16 KB / D-channel for signaling and control information, circuit-switched communication of voice, video, and data.

BRIDGE
A device that connects and passes packets between two network segments. Bridge operate at layer 2 of the OSI reference model - the Data Link layer - and are insensitive to upper-layer protocols.
- Interconnect 2 parts of a same network 
- Only read the destination addresses of each packets. Ethernet or Token-Ring. 

BROADBAND
Data-transmission technique that allows multiple simultaneous signals to share a transmission medium bandwidth by using radio frequency - rf - modulation. The total capacity of the medium is divided into multiple, independent bandwidth channels, where each channel supports an independent network and occupies a specific frequency range. Thus several networks are able to coexist on a single cable.
As contrasted with baseband, a transmission system that multiplexes multiple independent signals onto one cable.
In telecommunications terminology, any channel having a bandwidth greater than a voice-grade channel - 4kHz. 
In LAN terminology, a coaxial cable on which an analog signaling is used.

BROADCAST
A message sent to all nodes or an address for all nodes on a network.

BSC
Binary Synchronous Communication.
A data trans. protoc. for multiprotoc. backbone networks.

BSN
Backward Sequence Number

BT
Burst Tolerance - ATM

BTU
Basic Transmission Unit - SNAª 

BURST
Item from the signal transmitted inside a TDMA. time for a regular burst is 148 bits - 148*3/812500s-546 Us. For a burst access 88 bits - 88*3/812500=325 Us.

BUS TOPOLOGY
A network topology in which all nodes are connected to a single coaxial cable.

B2B
Business-to-Business - Any trade or relationship between two companies.

B2C
Business-to-Consumer - Any trade or relationship between two companies or consumers.

B2E
Business-to-Employee - Relation between the employee and the company.

BVCT
Basic Class Virtual Terminal - OSI

BYTE
Binary Term / Binary Digit Eight
8 bits.