Broadband

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This article is about the specific technical term. For the end user Internet access method see Broadband Internet access.

Broadband in general electronics and telecommunications is a term which refers to a signal or circuit which includes or handles a relatively wide range of frequencies. Broadband is always a relative term, understood according to its context. The wider the bandwidth, the more information can be carried. In radio, for example, a very narrowband signal will carry Morse code; a broader band will carry speech; a yet broader band is required to carry music without losing the high audio frequencies required for realistic sound reproduction. A television antenna described as "normal" may be capable of receiving a certain range of channels; one described as "broadband" will receive more channels. In data communications a modem will transmit a bandwidth of 64 kilobits per seconds (kbps) over a telephone line; over the same telephone line a bandwidth of several megabits per second can be handled by ADSL, which is described as broadband (relative to a modem over a telephone line, although much less than can be achieved over a fibre optical circuit, for example).

Broadband in data communications may have the same meaning as above, so that data transmission over a fibre optical cable would be referred to as broadband as compared to a telephone modem operating at 600 bits per second.

However, broadband in data communications is frequently used in a more technical sense to refer to data transmission where multiple pieces of data are sent simultaneously to increase the effective rate of transmission, regardless of actual data rate. In network engineering this term is used for methods where two or more signals share a medium.

Various forms of Digital Subscriber Line service are broadband in the sense that digital information is sent over one channel and voice over another channel sharing a single pair of wires. Analog modems operating at speeds greater than 600 bit/s are technically broadband. They obtain higher effective transmission rates by using multiple channels with the rate on each channel limited to 600 baud. For example, a 2400 bit/s modem uses four 600 baud channels (see baud). This is in contrast to a baseband transmission where one type of signal uses a medium's full bandwidth such as 100BASE-T Ethernet.

1 Multiplexing
2 Confusing usage
3 See also
4 External links

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Multiplexing

Communications may utilise a number of distinct physical channels simultaneously; this is multiplexing for multiple access. Such channels may be distinguished by being separated from each other in time (time division multiplexing or TDMA), in carrier frequency (frequency division multiplexing (FDMA) or wavelength division multiplexing (WDM)), or in access method (code division multiplexing or CDMA). Each channel that takes part in such a multiplexing exercise is by definition narrowband (because it is not utilising the whole bandwidth of the medium), whereas the whole set of channels taken together and utilised for the same communication could be described as broadband.

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Confusing usage

While many lower rate forms of data transmission, such as analog modems above 600 bit/s, are broadband, broadband has been more closely associated with higher data rate forms of broadband data transmission such as T-carrier and Digital Subscriber Lines. Therefore, the word "broadband" has also come to mean a relatively high rate, while the term "narrowband" is used to mean a relatively low rate. It is now quite common to hear a broadband method such as a 9600 bit/s modem described as "narrowband", while a high rate baseband transmission such as 10BASE-T is described as "broadband". The International Telecommunication Union Standardization Sector (ITU-T) recommendation I.113 has defined broadband as a transmission capacity that is faster than primary rate ISDN, at 1.5 to 2 Mbit/s. However speeds of 256 kbit/s and greater are commonly marketed as "broadband" and this convention is held to by policy makers and ISPs alike. See Broadband Internet access. Note: The term "narrowband" is also used to mean the opposite of "wideband" instead of the opposite of "broadband".

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