Broadband: Meaning (information, definition, explanation, facts)

A broadband medium is one that utilises the whole (or nearly whole) range of frequencies for communication that the medium can carry. Therefore it is difficult to send any more data over the medium than is already being sent, by frequency division multiplexing. This is the opposite of narrowband; both terms refer to the width of the band of frequency spectrum available for communication use. A channel may be broadband because it sends a signal without modulating it on a carrier, so the signal naturally covers the whole range of the frequency spectrum that the medium can carry - examples of this include buses in computers, serial and parallel connections, ethernet, IDE, SCSI, etc. A channel may be broadband because even though the signal is modulated on a carrier, it is done in a way to maximise the bandwidth over the channel - examples of this include ADSL (which splits up the signal into parts and sends each part over a separate carrier in order to maximise the usage of the frequency spectrum that the wire can carry).

Recently, the term Broadband has been hijacked by Internet Service Providers (ISPs) to refer to a particular style of Internet access, called broadband Internet, where the connection used for access is greater than a telephone modem (56 kbit/s). It is generally accepted that the term is used to mean a connection of 512kbit/s or above, though some Internet Service Providers have marketed services with a shorter bandwidth because there is no specific bitrate defined by the industry. On August 13, 2004 the ISP Wanadoo were told by the Advertising Standards Authority to change the way that they advertised their 512kbit/s broadband service in Britain, removing the words "full speed" which rival companies claimed was misleading people into thinking it was the fastest available service.

By the above definition, a telephone modem is a broadband connection (because it uses every trick in the book to carry 56 kbit/s over a link that has an ultimate bandwidth of 64 kbit/s), and a cable modem is a narrowband connection (because the data is modulated over a carrier signal somewhere between 20MHz and 500MHz - the ultimate bandwidth of the coaxial cable is huge), even though the cable modem connection can be forty times faster (or more) than the modem.

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.