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In telecommunications, broadband is a wide bandwidth data transmission with an ability to simultaneously transport multiple signals and traffic types. The medium can be coaxial cable, optical fiber, radio or twisted pair. In the context of Internet access broadband is used much more loosely; to mean any high-speed Internet access that is always on and faster than traditional dial-up access. ==Overview== Different criteria for "broad" have been applied in different contexts and at different times. Its origin is in physics, acoustics, and radio systems engineering, where it had been used with a meaning similar to "wideband".〔 Issued December 12, 1950.〕 Later, with the advent of digital telecommunications, the term was mainly used for transmission over multiple channels. Whereas a passband signal is also modulated so that it occupies higher frequencies (compared to a ''baseband'' signal which is bound to the lowest end of the spectrum, see line coding), it is still occupying a single channel. The key difference is that what is typically considered a ''broadband signal'' in this sense is a signal that occupies multiple (non-masking, orthogonal) passbands, thus allowing for much higher throughput over a single medium but with additional complexity in the transmitter/receiver circuitry. The term became popularized through the 1990s as a marketing term for Internet access that was faster than dialup access, the original Internet access technology, which was limited to 56 kbit/s. This meaning is only distantly related to its original technical meaning. In telecommunications, a broadband signaling method is one that handles a wide band of frequencies. "Broadband" is a relative term, understood according to its context. The wider (or broader) the bandwidth of a channel, the greater the information-carrying capacity, given the same channel quality. In radio, for example, a very narrow band will carry Morse code, a broader band will carry speech, and a still broader band will carry music without losing the high audio frequencies required for realistic sound reproduction. This broad band is often divided into channels or "frequency bins" using passband techniques to allow frequency-division multiplexing instead of sending a higher-quality signal. A television antenna may be described as "broadband" because it is capable of receiving a wide range of channels, while a single-frequency or Lo-VHF antenna is "narrowband" since it receives only 1 to 5 channels. The U.S. federal standard FS-1037C defines "broadband" as a synonym for wideband. In data communications a 56k modem will transmit a data rate of 56 kilobits per second (kbit/s) over a 4-kilohertz-wide telephone line (narrowband or voiceband). The various forms of digital subscriber line (DSL) services are ''broadband'' in the sense that digital information is sent over multiple channels. Each channel is at higher frequency than the baseband voice channel, so it can support plain old telephone service on a single pair of wires at the same time.〔(【引用サイトリンク】title=Broadband - Define Broadband at Dictionary.com )〕 However, when that same line is converted to a non-loaded twisted-pair wire (no telephone filters), it becomes hundreds of kilohertz wide (broadband) and can carry up to 60 megabits per second using very-high-bitrate digital subscriber line (VDSL or VHDSL) techniques. In the late 1980s, the Broadband Integrated Services Digital Network (B-ISDN) used the term to refer to a broad range of bit rates, independent of physical modulation details. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「broadband」の詳細全文を読む スポンサード リンク
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