Glossary - B

B8ZS

Bipolar 8 Zero Substitution (physical layer, communications)

Back Door (security)

A hole in the security of a system deliberately left in place by designers or maintainers. The motivation for such holes is not always sinister; some operating systems, for example, come out of the box with privileged accounts intended for use by field service technicians or the vendor's maintenance programmers.
Historically, back doors have often lurked in systems longer than anyone expected or planned, and a few have become widely known. The infamous RTM worm of late 1988, for example, used a back door in the BSD Unix "sendmail(8)" utility.
Ken Thompson's 1983 Turing Award lecture to the ACM revealed the existence of a back door in early Unix versions that may have qualified as the most fiendishly clever security hack of all time. The C compiler contained code that would recognise when the "login" command was being recompiled and insert some code recognizing a password chosen by Thompson, giving him entry to the system whether or not an account had been created for him.
Normally such a back door could be removed by removing it from the source code for the compiler and recompiling the compiler. But to recompile the compiler, you have to *use* the compiler - so Thompson also arranged that the compiler would *recognise when it was compiling a version of itself*, and insert into the recompiled compiler the code to insert into the recompiled "login" the code to allow Thompson entry - and, of course, the code to recognise itself and do the whole thing again the next time around! And having done this once, he was then able to recompile the compiler from the original sources; the hack perpetuated itself invisibly, leaving the back door in place and active but with no trace in the sources.
The talk that revealed this truly moby hack was published as ["Reflections on Trusting Trust", "Communications of the ACM 27", 8 (August 1984), pp. 761--763].

Backbone (network)

A primary transmission medium in a hierarchically distributed system; designed to interconnect and integrate a variety of voice, data and image networks with a diverse array of systems, equipment and applications.

BAL

French acronym for mailbox.

Balun

Balanced-unbalanced (network)
An impedance-matching device that connects a balanced line (such as a twisted-pair line) with an unbalanced line (such as a coaxial cable).

Bandwidth (network)

Measure of transmission capacity of a communications medium; measured differently for analog and digital transmissions. The greater the bandwidth, the more information that can be transmitted in a specified amount of time.

Bandwidth on Demand

The assignment of bandwidth to a trunk or circuit link as needed.

Baseband

The frequency band occupied by a single or composite signal in its original or unmodulated form.

BASize

Buffer Allocation Size (ATM)
A 1-byte field in the CPCS-PDU header to indicate to the receiving end the buffer space that needs to be reserved for reassembling the CPCS-PDU.

Batch (programming)

A term describing a system that takes a set (a "batch") of commands or jobs, executes them and returns the results, all without human intervention. This contrasts with an interactive system where the user's commands and the computer's responses are interleaved during a single run.
A batch system typically takes its commands from a disk file (or a set of punched cards in the old days) and returns the results to a file (or prints them). Often there is a queue of jobs which the system processes as resources become available.
Hackers use this somewhat more loosely than the traditional technical definitions justify; in particular, switches on a normally interactive program that prepare it to receive non-interactive command input are often referred to as "batch mode" switches. A "batch file" is a series of instructions written to be handed to an interactive program running in batch mode.

Baud (unit, network)

A unit of signaling speed equal to the number of signal events per second; not necessarily the same as bits per second.

BBS

Bulletin Board System (network)

BCD

Binary Coded Decimal (network)
6-bit code that allows 64 combinations to code alphanumeric caracters. Has been replaced by ASCII.

BCOB

Broadband Connection Oriented Bearer (ATM)

BCOB-A

Broadband Connection Oriented Bearer Class A (ATM)

BCOB-C

Broadband Connection Oriented Bearer Class C (ATM)

BCOB-X

Broadband Connection Oriented Bearer Class X (ATM)

BEC

Backward Error Correction (network)
An error-correction scheme where the sender retransmits any data to be found in error, based on the feedback from the receiver.

BECN

Backward Explicit Congestion Notification (network)
A bit in the frame relay header. The bit is set by a congested network node in any frame which is traveling in the reverse direction of the congestion (in frame relay, a node can be congested in one direction of frame flow but not in the other).

Bellcore

Bell Communications Research (network)
The research arm of the seven Bell Operating Companies which were originally part of AT&T. Bellcore was originally part of Bell Laboratories.

BER

Bit error Rate (network)

Basic Encoding Rules (ASN.1) (network)
Standard rules for encoding data units described in the Abstract Syntax Notation One (ASN.1). Sometimes incorrectly lumped under the term ASN.1, which properly refers only to the abstract syntax description language, not the encoding technique.

BES

Busty Errored Seconds (ATM)

Best Effort (ATM)

A QoS class in which no specific traffic parameters and no absolute guarantees are provided. Best effort includes UBR and ABR. See also service types.

BGP

Border Gateway Protocol (routing, network)

BICI - B-ICI

Broadband Inter-Carrier Interface (ATM)
A carrier-to-carrier interface similar to PNNI (private network-to-network interface) but lacking some of the detailed information offered by the latter. The difference arises because carriers are less likely to let their switches share routing information or detailed network maps with their competitors' gear. BICI now supports only PVCs (permanent virtual circuits) between carrier networks; the ATM Forum's BICI working group is currently addressing SVCs (switched virtual circuits).
An interface that supports service connections (such as CRS, CES, SMDS, FR) across public ATM networks and/or carriers.

BIP

Bit Interleaved Parity (physical layer, communications)

B-ISDN

Broadband aspects of Integrated Services Digital Network (network)
An ITU-T-introduced protocol platform to support the integrated, high-speed transmission of data, audio and video in a seamless fashion. ATM emerged as a suitable transport standard.

B-ISSI

Broadband Inter-Switching System Interface (network)

B-ISUP

Broadband ISDN User's Part (network)
A SS7 protocol which defines the signaling messages to control connections and services. It is used to establish, maintainand release broadband switched network connections accross an SS7/ATM network.

Bit

Binary digIT (general)
The smallest unit of information (data) and the basic unit in data communications.

BITS

Building Integrated Timing Supply (physical layer)

Bit Error (network)

The value of an encoded bit can be changed due to a transmission problem (e.g., noise on the line) and then interpreted incorrectly by the receiver.

Bit Rate

The number of bits of data transmitted over a communications line each second.

BNC

Bayonet-Neill-Concelman (hardware, network)
A bayonet-locking connector used to terminate coaxial cables.
A BNC connector has a bayonet-type shell with two small knobs on the female connector which lock into spiral slots in the male connector when it is twisted on.
BNC is also referred to as Bayonet Network Connector, Bayonet Navy Connector, British Naval Connector, Bayonet Nut Connection.

Bit/s - Bps

Bits per second (unit, network)
A measure of data transmission speeds. Notations: Bit/s, bps. See also Mbps, Gbps.

Body (communications,email, news, HTML)

In a message, name given to the part that contains the real message (what people want to say). It is different from the header that contains service and control information (sender, date, subject...) used to deliver or handle the message.
IN HTML, it is the name of the tag that delimits the data that is to be displayed.

BOF (communications)

Birds Of a Feather (network,standardization)
A Birds Of a Feather (flocking together) is an informal discussion group. It is formed, often ad hoc, to consider a specific issue and, therefore, has a narrow focus.
See also: Working Group.

BOM

Beginning of Message (network)
A PDU that constitutes the beginning of a message.

BONAPARTE

Broadband Optical Network using ATM PON Access facilities in Realistic Telecommunications Environments (ATM)

Boucle Locale

French equivalent for Local Loop.

BPDU

Bridge Protocol Data Unit (Datalink layer)

BPS

Bits per second (unit, network)
A measure of data transmission speeds. Notations: Bit/s, bps. See also Mbps, Gbps.

BV

BiPolar Violation (Physical layer)

BRI

Basic Rate Interface (network)
A kind of Integrated Services Digital Network channel consisting of two 64 Kbit per second "bearer" (B) channels for user-data transfer plus a 16 kbps "delta" (D) channel for control and signalling information. A BRI provides a total data rate of 144 kilobits per second. The B channels are used for voice or data, and the D channel is used for signalling and/or X.25 packet networking. BRI is the kind of ISDN interface most likely to be found in residential service.
See PRI.

Bridge (network)

A LAN interconnection device which forwards traffic between network segments based on datalink layer information. These segments would have a common network layer address. Bridges are used extensively in LAN systems to extend their physical dimensions or modify their performance. See also gateway, router.

Bridging (network)

Techniques for interconnecting two LAN segments that utilize the same LLC procedures but may use the same or different MAC procedures.

Broadband (communications, network)

Originally described the frequency bandwidth of analog circuits. Now used informally to describe any networking technology that employs high-speed digital circuits, generally over 1.544 Mbps.
The term applied to networks having bandwidths significantly greater (more than 64 kilobits per second) than that found in telephony networks. Broadband systems are capable of carrying a large number of moving images or a vast quantity of data simultaneously. Broadband techniques usually depend on coaxial or optical cable for transmissions. They utilize multiplexing to permit the simultaneous operation of multiple channels or services on a single cable. Frequency division multiplexing or cell relay techniques can both be used in broadband transmission.
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 or wide band.

Broadcast (network)

A message forwarded to all network destinations(multiple, unspecified recipients). On Ethernet, a broadcast packet is a special type of multicast packet which all nodes on the network are always willing to receive.

Brouter

Bridge-Router (network)
In local area networks, a device that combines the dynamic routing capability of an internetwork router with the ability of a bridge to interconnect LANs.

Browser (software)

A program that is used to look through a set of data.

Web Browser (www, Internet)
The client software that enables you to browse various kinds of Internet resources. Browsers can be both text-based or graphic. Netscape Navigator, Microsoft's Internet Explorer and derivatives of Mosaic represent about 90 percent of the graphic browsers on the market.

BSC

Binary Synchronous Communications (network)
datalink layer synchronous protocol introduced by IBM. It is replaced by SDLC.

BSI

British Standards Institute (standard, body)
British member of the ISO (International Standard Organisation).

BT

Burst Tolerance (ATM)
Proportional to the MBS, burst tolerance is used as a measure (leaky bucketparameter) for conformance checking of the SCR.

BTAG

Begin Tag (ATM)
8-bit field of the CPCS header in AAL3/4. This field is used to number CPCS modulo 256 and must be identical to the BTAG field.

B-TE

Broadband Terminal Equipment (ATM)
An equipement category for B-ISDN wich includes terminal adapters an terminals.

Buffer

Area in a device for temporary storage of data in transit; can accommodate differences in processing speeds between devices by storing data blocks until they are ready to be processed by a slower device.

Burst

Burstiness (ATM)

A source traffic characteristic that is defined as the ratio of the peak cell rate (PCR) to the average cell rate. It is a measure of the intercell spacing. See also MBS.

Bursty - Batchy

Communications characterized by high volumes of data transmitted intermitantly, as opposed to steady-stream data.

BUS

Broadcast and Unknown Server (ATM)
A server that forwards multicast,broadcast and unknown-destination address traffic to the attached LECs. ATM Forum-defined specifications in support of LAN-to-LAN connectivity, called LAN Emulation. The BUS is designed for carrying broadcast data, such as TCP/IP address resolution broadcasts or Novell Service Advertising Protocol (SAP) messages. It also handles all multicast traffic. Finally, it broadcasts the initial unicast frames sent by the LEC while the LES works in tandem to provide the appropriate ATM address for establishing a direct link.

Bus Topology

LAN topology with a single transmission path shared by every user. All nodes listen to all transmissions and select specific messages based on address identification; requires a contention-control mechanism for accessing the transmission medium.

Butineur

French (from Quebec) synonym of browser.

BW

Bandwidth (network)
See Bandwidth.

Bypass (communications)

Facilities Bypass: The use of facilities other than those of the local telephone company (LEC) (Facilities Bypass), using satellites and microwave systems for instance.
The service bypass is the use of operating telephone company private lines to connect a customer premise to a Point of Presence (POP) or another customer premise.

Byte (unit, network)

A sequence of adjacent binary data bits treated as a unit; 8 bits equal a byte; a byte is usually the smallest addressable unit of information in memory.
A byte may be 9 bits on 36 bit computers. Some older architectures used "byte" for quantities of 6 or 7 bits, and the PDP-10 and IBM 7030 supported "bytes" that were actually bit fields of 1 to 36 (or 64) bits! These usages are now obsolete, and even 9 bit bytes have become rare in the general trend toward power-of-2 word sizes. See also octet.

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