Broadband
This article is about the general technical term. For end user Internet access methods 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 (kbit/s) 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 optic circuit, for example).
Broadband in
data communications may have the same meaning as above, so that data transmission over a
fibre optic 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.
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.
*
Flat rate* http://www.cis.state.mi.us/mpsc/comm/broadband/broadband/broadband.htm
* http://www.itu.int/ITU-T
* US statistics on broadband subscribership http://www.fcc.gov/wcb/iatd/comp.html
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