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The term broadband refers to the wide bandwidth characteristics of a transmission medium and its ability to transport multiple signals and traffic types simultaneously. The medium can be coax, optical fiber, twisted pair, DSL local telephone networks or wireless. In contrast, baseband describes a communication system in which information is transported across a single channel.
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. 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 lowest end of 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. Finally, 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 kbps. This meaning is only distantly related to its original technical meaning.
Broadband refers to a communication bandwidth of at least 256 kbit/s. Each channel is 4 MHz wide and it uses an extensive range of frequencies to effortlessly relay and receive data between networks. 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; 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 US 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.
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 computer networks
Many computer networks use a simple line code to transmit one type of signal using a medium's full bandwidth using its baseband (from zero through the highest frequency needed). Most versions of the popular Ethernet family are given names such as the original 1980s 10BASE5 to indicate this. Networks that use cable modems on standard cable television infrastructure are called broadband to indicate the wide range of frequencies that can include multiple data users as well as traditional television channels on the same cable. Broadband systems usually use a different radio frequency modulated by the data signal for each band. The total bandwidth of the medium is larger than the bandwidth of any channel.
The 10BROAD36 broadband variant of Ethernet was standardized by 1985, but was not commercially successful. The DOCSIS standard became available to consumers in the late 1990s, to provide Internet access to cable television residential customers. Matters were further confused by the fact that the 10PASS-TS standard for Ethernet ratified in 2008 used DSL technology, and both cable and DSL modems often have Ethernet connectors on them.
Power lines have also been used for various types of data communication. Although some systems for remote control are based on narrowband signaling, modern high-speed systems use broadband signaling to achieve very high data rates. One example is the ITU-T G.hn standard, which provides a way to create a local area network up to 1 Gigabit/s (which is considered high-speed as of 2014) using existing home wiring (including power lines, but also phone lines and coaxial cables).
Broadband in analog video distribution is traditionally used to refer to systems such as cable television, where the individual channels are modulated on carriers at fixed frequencies. In this context, baseband is the term's antonym, referring to a single channel of analog video, typically in composite form with separate baseband audio. The act of demodulating converts broadband video to baseband video. Fiber optic allows the signal to be transmitted farther without being repeated. Cable companies use a hybrid system using fiber to transmit the signal to neighborhoods and then changes the signal from light to radio frequency to be transmitted to over coaxial cable to homes. Doing so reduces the use of having multiple head ends. A head end gathers all the information from the local cable networks and movie channels and then feeds the information into the system.
The standards group CCITT defined "broadband service" in 1988 as requiring transmission channels capable of supporting bit rates greater than the primary rate which ranged from about 1.5 to 2 Mbit/s. The US National Information Infrastructure project during the 1990s brought the term into public policy debates.
Broadband became a marketing buzzword for telephone and cable companies to sell their more expensive higher data rate products, especially for Internet access. In the US National Broadband Plan of 2009 it was defined as "Internet access that is always on and faster than the traditional dial-up access". The same agency has defined it differently through the years.
In 2000, 3% of the US adult population had access to a broadband connection at home. As of August 2013 70% of US adults accessed the Internet at home through a broadband connection, while 3% used dial-up.
Even though information signals generally travel between 40% and 70% of the speed of light in the medium no matter what the bit rate, higher rate services are often marketed as "faster" or "higher speeds". (This use of the word "speed" may or may not be appropriate, depending on context. It would be accurate, for instance, to say that a file of a given size will typically take less time to finish transferring if it is being transmitted via broadband as opposed to dial-up.) Consumers are also targeted by advertisements for peak transmission rates, while actual end-to-end rates observed in practice can be lower due to other factors.
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