B-Mac - This is a method of transmitting and scrambling television signals; the are time-multiplexed with a digital burst that contains digitized sound, video synchronizing, authorization, or information.

　　Backdoor - A way of getting into a guarded system without using the required password.

　　Backlog - The amount of work in process in the factory; it is usually expressed in terms of sales (sales backlog) or satellites (satellite backlog).

　　Backslash - This is the character "".

　　Backspace - This is the command that causes the cursor on your screen to move back one space, and it can or cannot delete characters.

　　Band Pass Filter - A circuit that will allow signals within a desired frequency band to pass through but prohibits signals outside this frequency band from penetrating.

　　Bandwidth - The range of frequencies, expressed in hertz (Hz), that can pass over a given transmission channel (thus, determining the rate at which information can be transmitted). In satellite based systems a larger bandwidth of 17.5 to 72 MHz is used to spread the television signal; this helps to prevent interference.

　　Baseband - The basic direct output signal, which is in an intermediatefrequency base and is obtained directly from a television camera, satellite TV receiver, or video recorder.

　　Baud - The rate of data transmission; it is based on the number of signal elements transmitted in a second. The term comes from the scientist J. M. E. Baudot.

　　BBS - This is an acronym for Bulletin Board Systems, which typically allow users to leave messages for other users.

　　Beacon - Relatively low-power carrier transmitted by a satellite, allowing the controlling engineers on Earth to monitor telemetry data or track the satellite.

　　Beamwidth - The angle or conical shape of the beam that the antenna projects. Since larger antennas have narrower beamwidths, they can pinpoint satellites in space or in dense traffic areas on the earth with more precision.

　　Bell 103 - This is an AT&T specification for a modem at speeds of up to 300 bps (bits per second). This is the most common standard for modems in PCs.

　　Bell 201 - The AT&T standard for 2400 bps modems.

　　Bell 202 - The AT&T standard for 1800 bps modems.

　　Bell 208 - The AT&T standard for 4800 bps modems.

　　Bell 209 - The AT&T standard for 9800 bps modems.

　　Bipropellant - Propellants are the fuel used in satellite propulsion systems. Bipropellant means that two fuels are used.

　　BISYNC - This refers to bisynchronous transmission.

　　Bit - This is a contraction of the term Binary digIT, and it is a number in base 2, which means that it can only be a 0 or a 1.

　　Bit Error Rate - The rate of message bits that are in error (an error rate of 106 means that there will be on average one error for every million bits).

　　Bit Rate - This is the speed of a digital transmission and is measured in bits per second.

　　Bitstream - This is data transmitted in a continuous stream (i.e., there are no breaks between characters).

　　Blind Dial - This is when a modem is instructed to dial a number without waiting for a dial tone (when connecting to a line with no dial tone).

　　Block - A group of bits transmitted as a single unit.

　　Block Down Converter - A device that is analogous in function to an electrical transformer and is used to drop the 3.7 to 4.2 KHz signal down to UHF or lower frequencies (i.e, 1 GHz and lower).

　　Board - This is a system on which you can view or leave messages.

　　Bps - This stands for Bits Per Second is a transmission rate.

　　Braces - These are the characters "{" and "}".

　　Break - This is merely an interruption of some sort.

　　Broadband - Data transmission of greater than 56 Kbps (kilo-bytes per second) that can carry multiple signals at once. The larger the bandwidth of a carrier, the greater the amount of information it can carry.

　　Broadbeam - A single large circular beam, which covers a large geographic area (opposite of the narrow beam produced by more powerful antennas).

　　Broadcast - The sending of one transmission to multiple users in a defined group, area, or region. See Multicast and Unicast.

　　Browse - To read through a list of messages or surf the internet (with a browser, such as Netscape or IE).

　　Buffer - This is the place in memory where the transmitted information is temporarily stored before transmission or after reception.

　　Bulletin Board System - This is an electronic message system, usually ran on a microcomputer.

　　Busy - When a phone line or service is used being used by someone.

　　Busy Signal - The sound that signifies that a phone line or service is in use (i.e., busy).

　　Byte - 8 bits.

　　补充：

　　Backbone - A series of high-speed network connections through which other networks connect.

　　Bandwidth - According to Webster's: a range within a band of wavelengths, frequencies, or energies; esp: a range of radio frequencies which is occupied by a modulated carrier wave, which is assigned to a service, or over which a device can operate. In Internet terms, bandwidth commonly refers to the amount of information that can be sent through a connection.

　　Bit - (binary digit) The smallest unit of computer information.

　　Browser - A software program that allows you to view HTML documents and navigate on the WWW.

　　Business Systems - The set of voice, data, and Internet products that provide communication solutions and services to business customers. The products usually reside within the customer's place of business.

　　Byte - A combination of bits that represents a single character (approximately 8 bits equal one byte).
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