1. A capital B stands for Byte. A small b stands for bit. Typically a byte is eight bits (but it could be more or fewer). Virtually all telecommunications transmission ” data, voice or video, etc. ” is stated in bits per second (bps, or b/s). Virtually all transmission inside a computer (like movement between a disk and the computer's central microprocessor is written in bytes per second. Thus Mbps would be million bits per second, while MBps would be million bytes per second. For a much longer explanation, see the introduction. See also Bit and Byte.

  2. The local wireline cellular carrier. In one of its less intelligent decisions, the Federal Communications Commission decided to issue two cellular franchises in each city of the United States. They gave one to the local phone company (the B carrier) and one to a competitor (the A carrier). This duopoly has naturally meant little real price competition. At least it did until the FCC issued PCS (Personal Communications Services). licences and competition started. See PCS.

  3. Beta. As in beta test. A beta test is a test of a product in a real production environment with a real, live customer. Beta tests come after alpha tests, and before the general release of the product.

B 1

See B-1.

B Battery

A section of a phone system power supply that provides unfiltered Direct Current for operating relays and various other components . Typically 20 volts . See A Battery.

B Bit

See A & B Bits.

B Carrier

A cellular carrier operating in the 869-894 MHz range. In U.S. markets that have only two cellular carriers , one is designated the A carrier and the other the B carrier, which operates in the 869-894 MHz range. The "B" band license was generally awarded to the wireline telephone operator in the market and, hence, the B Carrier was historically referred to as the "wireline" license.

B Channel

A "bearer" channel is a fundamental component of ISDN interfaces. It carries 64,000 bits per seconds in both directions, is circuit switched and is able to carry either voice or data. Whether it does or not depends on how your local telephone company has tariffed its ISDN service. See Basic Rate Interface (BRI) and ISDN.

B Connector

A commonly-used wire-splicing device consisting of a flexible plastic sleeve over a toothed metal cylinder that bites through insulation when crimped with pliers or a special crimping tool. It is about one inch long and can hold three or four wires. A gel- filled version (water-retardant jelly ) is available for installation in damp or humid areas. B connectors are also known as chiclets, beans, beanies, and rodent rubbers.

B Frame

Bi-directional or B frames (often called B pictures) refer to part of the MPEG video compression process whereby both past and future pictures / frames are used as references. B frames typically produce the most compression.

B Interface

An interface used in Cellular Digital Packet Data (CDPD) which is deployed over AMPS. The B interface connects the Mobile Data Intermediate System (MDIS) to the Mobile Data Base System (MDBS).

B Links

A SS7 term . Bridge links assigned in a quad arrangement. Bridge Link. A CCS/SS7 signaling link used to connect STP (Signal Transfer Point) pairs that perform work at the same functional level. These links are arranged in sets of four (called quads ). A minimum of three-way path diversity is recommended to allow three completely separate paths. The B-Links are assigned so that local Signal Transfer Points (STPs) can communicate with other local STPs or mated pairs of STPs at the same hierarchical level: local to local, regional to regional, or mated pair to mated pair.

B Number

A cellular term for the number of the called party. The originating switch analyzes the A Number (the number of the calling party) in order to route the call to the B Number.

B Port

The port which connects the outgoing primary ring and the incoming secondary ring of the FDDI dual ring. This port is part of a dual attached station or concentrator. See FDDI.


Brown and Sharp Gauge. See AWG (American Wire Gauge).


An unassociated central office line or a central office line that is not in rotary hunt that is used for a business line or a business fax/modem.


Basic 911. There is also an E-911, which stands for Enhanced 911. B-911 is a centralized emergency reporting system which may have many features but which does NOT provide ALI (Automatic Location Information) to the 911 operator. In most cases, it does not provide ANI (Automatic Number Identification) either. B-911 provides a common emergency response number and relies on Emergency Hold and Forced Disconnect to maintain effective service. See 911 for a full explanation.


Cellular licenses received from the FCC with an initial association to a telephone company. Also referred to as wireline.

B-Block Carrier

A 30-MHz PCS carrier serving a Major Trading Area (MTA) in the frequency block 1870-1885 MHz paired with 1950-1965 MHz.


Broadband Code Division Multiple Access.


A symmetric cryptographic algorithm designed by British Telecom.


Broadband Digital Cross-connect System. B-DCS is a generic term for an electronic digital cross-connect system capable of cross-connecting signals at or above the DS3 rate.


B-ISDN Inter-Carrier Interface: An ATM Forum defined specification for the interface between public ATM networks to support user services across multiple public carriers.


B-ICI Signaling ATM Adaptation Layer: A signaling layer that permits the transfer of connection control signaling and ensures reliable delivery of the protocol message. The SAAL is divided into a Service Specific part and a Common part (AAL5).


Broadband ISDN. A very vague term that defines a communications channel as anything larger than a single voice channel of 64 Kbps. Under this terminology, "broadband" can be as little as two voice channels. The official ITU-T recommendation I.113 [45] defines Broadband ISDN as "a service or system requiring transmission channels capable of supporting (transmission) rates greater than the primary rate [DS1]." Thus, broadband ISDN is a new concept in information transfer, although exactly what it is isn't clear yet. There is some discussion that broadband ISDN begins at 155 Mbps (the OC-3 version of SONET/SDH). In another ITU-T recommendation (I.121 [47]), the ITU-T presents an overview of what it sees as B-ISDN capabilities:

"B-ISDN supports switched, semipermanent and permanent point-to-point and point-tomultipoint connections and provides on demand, reserved and permanent services. Connections in B-ISDN support both circuit mode and packet mode services of a monoand/or multi-media type and of connectionless or connection-oriented nature and in a bidirectional or unidirectional configuration. A B-ISDN will contain intelligent capabilities for the purpose of providing advanced service characteristics, supporting powerful operation and maintenance tools, network control and management." The ITU-T (nee ITU) was to decide on an international standard for B-ISDN by 1996, although it has not yet been released. The ITU-T has defined two types of services in the context of B-ISDN, Interactive and Distribution. For a definition of those services, See Interactive Services and Distribution Services.

Bellcore says that "National and international standards bodies have made the Asynchronous Transfer Mode (ATM) the target solution for providing the flexibility required by B-ISDN. ATM provides a common platform capable of supporting both broadband and narrowband services ... The physical layer-transmission standard for B-ISDN is the Synchronous Optical Network (SONET), also known as the Synchronous Digital Hierarchy (SDH)." See N-ISDN and SONET.

B-ISDN Inter-Carrier Interface

An ATM Forum specification for a public UNI (User Network Interface) providing the interface via PVCs between public ATM networks to support user services across multiple public carriers. See UNI.


Broadband Integrated Services Digital Network user part. See ISDN and ISUP.


Broadband Lower Layer Information: This is a Q.2931 information element that identifies a layer 2 and a layer 3 protocol used by the application.


Broadband Personal Communications Services. The FCC designated 140 MHz in the 1850-1990 MHz range for PCS services. The B-PCS auctions ended in 1995, yielding over $7 billion in revenues to the U.S. government. B-PCS is intended to support features such as "follow-me." See also 500 Service and PCS.


Bi-directionally predictive-coded; an MPEG term for a picture that is coded using compensated prediction from a past and/or future reference picture.


Broadband Terminal Adapter. A form of DCE which provides the interface into a BISDN network from B-TE2, which is Terminal Equipment not compatible with the B-ISDN network.


Broadband Terminal Equipment: An equipment category for B-ISDN which includes terminal adapters and terminals.


See Broadband Wireless Local Loop.


Busy/Idle bits.


Business to Business. A term that defines a company selling its wares to other businesses and buying its wares from other businesses, as against selling its wares to consumers, which is B2C. One of the strongest B2B areas is setting up systems for companies to buy their supplies from other companies, using the Internet to streamline the process. Here is a neat piece from Ariba, one of the leaders in this field: In today's economy, where the new Internet rules apply, how can companies ensure that they will be winners? The answer is to leverage the Internet to gain a closer alignment with customers and partners , to integrate supply chains, and to take advantage of new revenue opportunities. Only by embracing the change and using it for competitive advantage will the bricks -and-mortar companies of today become the dot-com companies of tomorrow. Today, eCommerce is about using the Internet to gain competitive advantage, not only by improving the efficiency and effectiveness of existing business processes, but also by enabling constant adaptation to rapidly changing competitive landscapes .

Despite these imperatives for moving business on-line, today a single corporate purchase is still quite cumbersome and costly. AMR estimates that the cost per procurement transaction ranges from US$75 to US$175, often exceeding the cost of the items being purchased. This staggering fact results from most transactions happening via a complex, paper- intensive request, approval, and order process with high administrative costs and no economies of scale. These processes often include the re-keying of information, lengthy approval cycles, and significant involvement of financial and administrative personnel, often resulting in delays to end-users and productivity losses. Beyond the time and expense associated with manual processing costs, organizations suffer even greater costs when they cannot fully leverage procurement economies of scale. Most organizations lack the systems that enable them to monitor purchases and compile data necessary to negotiate better volume discounts with preferred suppliers. In addition, most organizations suffer from a problem known as "maverick buying," which occurs when personnel do not follow internal guidelines as to which suppliers to use for operating resource purchases. When employees do not buy from preferred suppliers, organizations pay a premium. AMR estimates that maverick buying accounts for one-third of operating resource expenditures, costing organizations a 15% to 27% premium on those purchases. In addition, low visibility into spending patterns and limited information further limit the benefits of volume procurement contracts.

Traditional procurement processes also result in missed revenue opportunities and additional costs to suppliers. When buyers are unable to channel purchases to preferred suppliers, these suppliers lose revenue. Suppliers also suffer from inefficient, error prone and labor-intensive order fulfillment processes. Many suppliers dedicate significant resources to the manual entry of information from faxed or phoned-in purchase orders and the manual processing of paper checks, invoices and ship notices. Suppliers also spend significant resources on customer acquisition and sales costs, including the production and distribution of paper catalogs. Without fully automated and integrated electronic commerce technologies, both buyers and suppliers incur substantial extraneous costs in conducting commerce.

Business-to-business eCommerce addresses these issues by providing a modern, electronic infrastructure that allows corporations to manage their internal and external procurement processes strategically. Business-to-business eCommerce leverages technology, lowering transaction costs through electronic commerce, automation, and use of decision support techniques to identify opportunities to rationalize the supply chain. By adopting business-to-business eCommerce, companies can build strategic supplier relationships and use aggregate buying to gain volume discounts from suppliers.


Business to Consumer. A term that defines a company selling its wares to consumers, as against selling its wares to other businesses, which is B2B. See B2B.


Bipolar with 3-Zero Substitution. The line coding technique used in the SONET STS- 1 (Synchronous Transport Signal-Level 1) electrical signal, which is then converted to an optical signal for transmission over the SONET optical fiber transmission system. B3ZS looks for a series of 3 consecutive zeros, removes them, and replaces them with either B0V or 00V. The choice between B0V and 00V is such that the number of B pulses between consecutive V pulses is odd, where B represents the normal bipolar pulse and V represents a bipolar violation. See also B8ZS, Bipolar Violation, SONET and STS.


A reader asked us if we knew what this term meant. Ray Horak, who's the best, emailed me, "I can find only three mentions of this anywhere , and no details. I suspect that it is an example of a "jam bit 7" process. This is an earlier, nonstandard feature that was used in DDS channels and channel banks, again, to preserve 1's density. The deal was that if the DS-0 carried a DDS formatted data channel, the least significant bit was a signaling bit and could often be 0. If the "data" were all 0's, then the entire byte could be all 0's. The third time in a row that an all-0 byte came up it would violate the 15-0's limit, so the channel bank would "jam" a 1 into the least significant bit (that is bit 7, if you count 0-7, which is the way we count them, rather than 1-8). This didn't affect data (which was 56 kilobits per second in the seven most significant bits) nor the signaling (which required every signal to be repeated multiple (7?) times before it meant anything to the receiver)."


Bipolar with 8 Zero Substitution. A technique specified in the ITU-T G.703 recommendation, B8ZS is used in North American T-1 circuits to accommodate the ones density requirement in the public network. B8ZS inserts one of two special violation codes for strings of eight consecutive zero voltage states, with the intentional bipolar violation codes being inserted in bit positions 4 and 7 of the datastream. The bipolar violation codes are of opposite polarity, thereby preventing the buildup of excessive DC voltage levels, with the specific bipolar violation code depending on the polarity of the preceding pulse. B8ZS, which generally is used on newer T-1 and ISDN PRI circuits, offers clear channel communications of 64 Kbps per channel. AMI (Alternate Mark Inversion) the older technique, suffers from a loss of timing recovery when 8 consecutive zeros are transmitted. E-1 standards utilize HDB3 (High Density Bipolar 3) line coding, which also is specified in G.703. See also AMI and HDB3.


Business Address.


Blanket Authorization Agreement. Signed by interconnectors guaranteeing that they have authority of the end user customer to request CPNI and place service orders on the customer's behalf . CPNI is Customer Proprietary Network Information. It's information pertaining to a customer's selected service arrangements with a bell operating company. This information is only available to competitors when written authorization from the customer is provided.

Babbage, Charles

1791 to 1871. An English researcher who contributed a great deal to the theory and practice of computing and conceived his now-famous 'analytical engine' ” an early computer.


Just what it sounds like ” crosstalk from several interfering communications circuits or channels.

Babbling Tributary

"A station that continuously transmits meaningless messages," as defined by John McNamara, of DEC and author of "Local Area Networks, an introduction to the technology." Some people might argue this was another word for Harry Newton, the author who didn't know when to stop and wanted to make this dictionary the most comprehensive telecom dictionary ever.


British Approvals Board for Telecommunications. You need their approval before you can sell telecom equipment in Great Britain.

Baby Bells

A term for the RBOCs (Regional Bell Operating Companies), also known as RHCs (Regional Holding Companies). The seven RBOCs were spun off from AT&T (the Bell System) in 1984, as a result of the MFJ (Modified Final Judgement), also known as The Divestiture Agreement. The original seven Baby Bells were Ameritech, Bell Atlantic (since merged with GTE to form Verizon), BellSouth, NYNEX (since acquired by Bell Atlantic), Pacific Telesis (since acquired by SBC), Southwestern Bell (now SBC) and US West (since acquired by Qwest). See also Divestiture.

Baby Bills

  1. A term for the numerous companies formed by ex-employees of Microsoft. A play on the "Baby Bell," the reference is to Bill Gates, co-founder and chairman of Microsoft.

  2. A term for the many companies that the Federal Government might split Microsoft into, as a result of the Microsoft antitrust case.


Feature allowing calls to an off-hook telephone to listen to room noises, for example, to check if a baby is crying.

Back Board

A piece of plywood mounted on a wall. Phone equipment is mounted on the plywood. It is more efficient to first mount phone equipment on plywood in the service bay, test it out while it's convenient and diagnostic tools are handy. Then take the phone equipment and the back board (which typically consists of the KSU, power supply and 66-blocks) and install them on the customer's premises. This "pre-installation" makes enormous sense ” economically and reliably. Sadly, few installation companies do it.

Back Box

Think of your half-built office or house. The rooms have been framed out. There are metal or wooden studs going from the ceiling to the floor. Soon you will attach sheetrock on either side of the studs and form your finished walls. But before you do, you need to string cables through the walls. In each room you'll want a bunch of electrical outlets. You make those electrical outlets by attaching a a metal or plastic box to the metal or wooden stud. That box is typically three inches or so deep and has an opening that is 2" x 3 1/2." In electrical and telecom industry terminology that box is called a "back box" or a single gang receptable box. By attaching various face plates to it and changing the insides, you can make your back box deliver electricity, cable TV, telephone, local area network and/or broadband service. You can also get back boxes in a double width, which is known (surprise, surprise) as a double gang receptacle box. In a normal electrical installation a single gang box would have two 120 volt A/C outlets, and a double gang box would have four. In a telecom installation a single gang receptable could contain as many as six telecom outlets, e.g. a couple of coaxial cables, a couple of phones and a couple of local area network connections for your computer and your networked printer.

Back Door

A way of getting into a password-protected systems without using the password. Usually a carefully guarded secret to prevent abuse and misuse.

Back End

First we have the front end and then we have the back end. Obviously if you think about either, both terms are totally meaningless. But people pretend they mean something. For example, one competitive dictionary (and a not a good one at that) defines back end as node or software program that provides services to a front end. (You figure what that means.) See also client, FRF.11, and server. Another dictionary defines back end as dDatabase server functions and procedures for manipulating data on a network.

Back End Processor

A server is often called a back end and a workstation is often called the front end. On a LAN (Local Area Network), a back end processor runs on a server. It is responsible for preserving data integrity and handles most of the processor- intensive work, such as data storage and manipulation.

Back End Results

A call center/marketing term. Used to describe the number of trial or risk free orders that actually pay in terms of customer orders. In a telephone sales context, a bad back-end can be the result of the reps selling the trial and not the product. See Front End Results.

Back Feed Pull

Used in tight locations where it's difficult to take large cable pulling equipment. The cable is fed in two parts from the mid-point. The first section of cable is fed in one direction. After this is fed, the remaining cable is unreeled and fed through the opposite direction to the other end point.

Back Haul

Back haul is a verb. A communications channel is back hauling when it takes traffic beyond its destination and back. There are many reasons it might do this. The first is that it may be cheaper to go that route instead of going directly. You might, for example, have a full-time private line from New York to Dallas. You might find it cheaper to reach Nashville by going to Dallas first, then dialing back to Nashville. The economics of backhauling may change from one moment to another as the line to Dallas is empty, close to full or full. Another reason for back hauling is that you may do it to accommodate changes in your calling or staffing patterns. You may have an automatic call distributor in Omaha and one in Chicago. A call from New York may come into your Omaha ACD, but when it gets there you may discover that there are no agents available to handle the call. So it may now make sense to back haul the call to the Chicago ACD, where an agent is available. In fiber networks, back hauling is a traffic management technique used to reduce the expense of multiplexing/ demultiplexing .

Back Hoe Fade

The degradation in service experienced when a backhoe cuts your buried fiber optic cable. Called fade because sometimes not all communications are cut off. Also, when they are all cut off, the term becomes a euphemism. Better to report a back hoe fade to your boss than to say, "We just lost 158,000 circuits between New York and Washington. Our customers are not pleased." See also Backhoe Fade for another variation.

Back Lobe

In a directional antenna, there is a main lobe and there may be additional lobes , one of which extends backward from the direction of the channeled signal, called a back lobe.

Back Office Operations

Management and support tasks that can be performed away from a company's headquarters, such as telemarketing, credit card processing, data file maintenance and many clerical and accounting functions. Back office operations are an economic development opportunity for small communities that have the appropriate infrastructure (e.g. advanced telecommunications, reliable express mail services.) Back office operations are helping share a new definition of place, one in which, for example, geographic remoteness is no longer a liability ” because of telecommunications and other linkages to the "outside" world.

Back Porch

The portion of a video signal that occurs during blanking from the end of horizontal sync to the beginning of active video. The blanking signal portion which lies between the trailing edge of a horizontal sync pulse and the trailing edge of the corresponding blanking pulse. Color burst is located on the back porch.

Back Pressure

Propagation of network congestion information upstream through an internetwork.

Back Projection

When the projection is placed behind a screen (as it is in television and various video conferencing applications where the image is displayed on a monitor or a fabric screen) it is described as a back projection system. In these systems the viewer sees the image via the transmission of light as opposed to reflection used in front projection systems. Audiences generally prefer back projection systems since they seem brighter.

Back scatter

An RFID definition. A method of communication between tags and readers. RFID tags using back-scatter technology reflect back to the reader a portion of the radio waves that reach them. The reflected signal is modulated to transmit data. Tags using back scatter technology can be either passive or active, but either way, they are more expensive than tags that use inductive coupling.

Back to Back Channel Bank

The connection of voice frequency and signaling leads between channel banks to allow dropping (i.e. removing) and inserting (i.e. adding) of channels.

Back to Back Connection

A connection between the output of a transmitting device and the input of an associated receiving device. When used for equipment measurements or testing purposes, this eliminates the effects of the transmission channel or medium.

Back to Back Peering

Peering is when large ISPs (Internet Service Providers) assume that the traffic is approximately equal between them, and both benefit equally from a free connectivity between them since both companies need each other's network to get people to their web sites. These ISPs allow traffic from these large ISPs to enter their network for free. Companies that are allowed into this prestigious club are called Tier 1 providers. They include Sprint, CAIS, UUNet, PSINet (the first and largest independent commercial ISP in the world), Cable and Wireless, etc. Companies that do not have large enough networks have to pay Tier 1 companies to get access to their networks.

Back to Square One

Back to square one (or "back at square one," which was the original way of saying it) comes from football radio commentaries from the 1930s. There being no picture, these live reports would explain the position of play by dividing the football pitch into numbered grids. Square one was just in front of the goal. So, when a ball went out of play and resulted in a goal kick, the play was "back at square one." Neat.

Back Up Server

A program or device that copies files so at least two up-to-date copies always exist.

Back-end System

The server part of a client/server system that runs on one or more file servers and provides services to the front-end applications running on networked workstations. The back-end system accepts query requests sent from a front-end application, processes those requests , and returns the results to the workstation.


The backbone is the part of the communications network which carries the heaviest traffic. The backbone is also that part of a network which joins LANs together ” either inside a building or across a city or the country. LANs are connected to the backbone via bridges and/or routers and the backbone serves as a communications highway for LAN- to-LAN traffic. The backbone is one basis for design of the overall network service. The backbone may be the more permanent part of the network. A backbone in a LAN, a WAN, or a combination of both dedicated to providing connectivity between subnetworks in an enterprise-wide network.

Backbone Bonding Conductor

A copper conductor extending from the telecommunications main grounding busbar to the farthest floor telecommunications grounding busbar.

Backbone Cabling

Cable and connecting hardware that comprise the main and intermediate cross-connects, as well as cable runs that extend between telecommunications closets, equipment rooms and entrance facilities.

Backbone Closet

The closet in a building where the backbone cable is terminated and cross connected to either horizontal distribution cable or other backbone cable.

Backbone Facilities

Plant and equipment used to provide transmission services to connect tributary facilities from clusters of dispersed users or devices. See Backbone.

Backbone Network

The part of a communications facility that connects primary nodes; a primary shared communications path that serves multiple users via multiplexing at designated jumping-off points. A transmission facility, or arrangement of such facilities, designed to connect lower speed channels or clusters of dispersed users or devices.

Backbone Router

A high-capacity system that directs and forwards information across a backbone network typically comprising leased lines. Data are directed across the network based on information contained in Layer 3 of the OSI Reference Model. The system can also be used to connect multiple LANs in a corporate campus network.

Backbone Subsystem

See Riser Subsystem.

Backbone To Horizontal Cross-Connect

BHC. Point of interconnection between backbone wiring and horizontal wiring.

Backbone Wiring

The physical/electrical interconnections between telecommunications closets and equipment rooms. Cross-Connect hardware and cabling in the Main and Intermediate Cross-Connects are considered part of the backbone wiring.


A phone fraud term. Backcharging is starting the clock on a phone call at the time a customer contacts the long- distant phone service provider ” not when the person being called answers the phone ” which is what it should be.

Backfeed Pull

A method used to pull cable into a conduit or a duct liner when the cable is long or when placing cable into controlled environmental vaults, central offices, or under streets . With this method, the cable pays off its reel at an intermediate manhole and is first pulled in one direction. The remaining cable is then removed from the reel, laid on the ground, and then pulled in the opposite direction.

Backfile Conversion

The process of scanning in, indexing and storing a large backlog of paper or microform documents in preparation of an imaging system. Because of the time-consuming and specialized nature of the task, it is generally performed by a service bureau .


To designate memory on an expanded memory card and make it available for use as conventional memory.


See Background Processing.

Background Area of Concern, Consequence and Incentive

BACI. A questioning strategy used by Lucent Technologies for uncovering a customer's implied needs and converting them to clearly defined ones that may lead to a purchasing decision.

Background Communication

Data communication, such as downloading a file from a bulletin board, that takes place in the background while the user concentrates on another application (e.g. a spreadsheet) in the foreground.

Background Music

This feature allows music to be played through speakers in the ceiling and/or through speakers in each telephone, throughout the office, or office-by- office, or selectively. Background music is typically played through paging speakers, but it can also be played through the speakers of speakerphones. In fact, the two ” paging and background music ” often go hand-in-hand. When you want to page someone, the music turns off automatically and comes back on when the paging is over. The same thing happens on airplanes. Background music is said to motivate workers, often into shutting it off.

Background Noise

The noise you hear when nothing else is being transmitted. Digital circuits are so quiet that some form of White Noise must be injected into them so as to prevent people from suspecting that the circuit they're speaking on has gone dead. See also White Noise.

Background Noise Regeneration

A technique for eliminating background noise bandwidth requirements.

Background Processing

The automatic execution of lower priority computer programs when higher priority programs are not using the computer's resources. A higher priority task would be completing calls. A lower priority task would be running diagnostics. Some PBXs have this feature. Some insist on running their diagnostics even though they are choked with calls. The smarter ones tone down their diagnostics when they get busier, which makes sense.

Background Program

A low priority program operating automatically when a higher priority (foreground) program is not using the computer system's resources.

Background Task

A secondary job performed while the user is performing a primary task. For example, many network servers will carry out the duties of the network (like controlling who is talking to whom) in the background, while at the same time the user is running his own foreground application (like word processing). See also Background Processing.


See Back Haul.

Backhoe Fade

Signal loss caused by some moron who forgot to call before he dug. Usually involves a fiber cut about the size of a backhoe blade . Typically affects a large number of very peeved customers and a small number of overworked Network Operations folks supported by the ever-encrusted Cable Cowboys called to the scene. Murphy's Law will ensure that Skillet with the Caterpillar made sure that he pulled the fiber as far out of the hole as possible so that it stretched the jacket inducing NUMEROUS breaks along it's (still- buried) length. Murphy would also state that a flood occurring before repairs are completed at the location is likely as well. Definition courtesy Todd Timlake. See Back Hoe Fade.


When a device attempts to transmit data and it finds trouble, the sending device must try again. It may not try again immediately. It may "back off" for a little time so the trouble on the line can be cleared. This happens with LANs. For example, an earlier attempt to transmit may have resulted in a collision in a CSMA/CD (Carrier Sense Multiple Access/Collision Detection) Local Area Network (LAN). So the device "backs off," waits a little and then tries again. How long it waits is determined by preset protocols.

Backoff Algorithm

The formula built into a contention local area network used after collision by the media access controller to determine when to try again to get back onto the LAN. See also Backoff.


The physical area, usually at the rear of an electronics frame, where modules and cables plug into the system. The high-speed communications line to which individual components, especially slide-in cards, are connected. For example, all the extensions of a PBX are connected to line cards (circuit boards ) which slide into the PBX's cage. At the rear of the PBX cage, there are several connectors. Each of these connectors is wired to the PBX's backplane, also called a backplane bus. This backplane bus is typically running at a very high speed, since it carries many conversations, address information and considerable signaling. These days, the backplane bus is typically a time division multiplexed line ” somewhat like a train with many cars , each representing a time slice of another conversation (data, voice, video or image). The backplane's capacity determines the overall capacity of the switch. See Passive Backplane.

Backplane Bus

See Backplane.


Propagation effects in a communications network of hop-by-hop flow control to upstream nodes.


In cases where light is launched into an optical fiber in a forward direction, backreflection refers to the light that is returned to the launch point in the reverse direction.


See Acronym.


  1. In fiber optics, the return of a portion of the scattered light signal to the input end of the fiber. Conceptually, backscattering is similar to echo. See also echo.

  2. Radio wave propagation in which the direction of the incident and scattered waves resolved along a reference direction (usually horizontal) are oppositely directed. A signal received by backscattering is often referred to as "backscatter."

Backside Bus

The bus (i.e., common electrical path) within the microprocessor that connects the CPU (Central Processing Unit) of a PC with the Level 2 cache memory. See also Cache and Frontside Bus.


Also called a virgule, the backslash key achieved fame because Microsoft used it to distinguish between subdirectories in MS-DOS. This is a backslash \.


A copy of computer data on an external storage medium, such as a floppy disk or tape. Computers and telephone systems (which are computers) are unreliable. They glitch and lose data for all sorts of unusual and impossible -to-predict reasons. Thus the necessity for backups . The theory is that when, not if, a glitch occurs the PBX's database will disappear off the face of the earth. If this happens, you have a backup. Simply retrieve it, load it up and, presto, you're back live.

Only information changed (since the backup was made) is lost. Backups save time in restoring the system after a loss. Most modern PBXs work with a database and other extensive customized instructions the user loads in. Most PBX users forget to make and keep backups of their PBX data. They expect their vendor to make backups, but he rarely does. This carelessness costs weeks of aggravation, as the PBX's database and instruction set is manually (and painfully) put back together.

The method by which backups are maintained is also important. The medium should clearly be reliable, i.e. the best quality magnetic medium. The method of backing up is also important. For example, a streaming tape backup is less reliable than a file-by-file backup. In a streaming backup, the backup medium simply captures the original data one bit after another in one long stream. In a file-by-file backup, the data moves over in logical segments ” command files, data files, etc. Streaming backups will work if their data is placed back on the same precise device from which they were originally taken. But, if they are placed on a different device (even though the same model number, etc.), they may barf because the tape assumes bad sectors are in the same place. This will probably not be true. Streaming tape backup devices are less expensive to buy and much faster to use. Avoid them.

Backup Domain Controller

BDC. A server in a network domain that keeps and uses a copy by a computer without interrupting its current or primary task. For Windows NT Server domains, refers to a computer that receives a copy of the domain's security policy and domain database, and authenticates network logons .

Backup Link

A resilient (fault tolerant) link which is not used until the primary link fails.

Backup Ring

The token ring cabling between MAUs or CAUs consists of the main ring and the backup ring. The data is normally transmitted on the main ring, but if an error occurs, the data can be transmitted on the backup ring until the main ring is repaired. In MAU networks the switching is done manually while in CAU (or CAM) networks it is done automatically.

Backward Channel

In data transmission, a secondary channel whose direction of transmission is constrained to be opposite to that of the primary (or forward) channel. The direction of transmission in the backward channel is restricted by the control interchange circuit that controls the direction of transmission in the primary channel. The channel of a data circuit that passes data in a direction opposite to that of its associated forward channel. The backward channel is usually used for transmission of supervisory , acknowledgement , or error-control signals. The direction of flow of these signals is opposite to that in which information is being transferred. The bandwidth of this channel is usually less than that of the forward channel, i.e., the information channel.

Backward Compatible

A general term applied to new technologies, products or services which represent a more or less graceful upgrade of those existing. As such, they can be provisioned without requiring dramatic and complete (read prohibitively expensive) changes in the current order of things. For instance, a new and enhanced PBX system technology can be implemented through an upgrade of the existing system rather than a full replacement. Although such an upgrade can be quite expensive, the investment in the current system is protected to a large extent from technical and functional obsolescence. Another example of backward compatibility is that of Frame Relay, which is based on the existing network infrastructure, including LAP-D, the link access protocol used in ISDN. Frame relay services, therefore, work over existing access links and make use of network standards already in place.

Backward Learning

Algorithmic process used for routing traffic that surmises information by assuming symmetrical network conditions. For example, if node A receives a packet from node B through intermediate node C, the backward-learning routing algorithm assumes that A can reach B through C optimally.

Backward Recovery

The reconstruction of an earlier version of a file by using a newer version of data recorded in a journal.

Backward Signal

A signal sent in the direction from the called to the calling station, or from the original communications sink to the original communications source. The backward signal is usually sent in the backward channel and consists of supervisory, acknowledgement, or error control elements.

Backward Supervision

The use of supervisory sequences from a secondary to a primary station.


Billing Account Cross Reference. The reference number correlating to the account of the LEC or LECs rendering matching bills in a meet point bill environment.

Newton[ap]s Telecom Dictionary
Newton[ap]s Telecom Dictionary
ISBN: 979387345
Year: 2004
Pages: 133

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