DSL or xDSL, is a family of technologies that provide digital data transmission
over the wires of a local telephone network. DSL originally stood for digital
subscriber loop, although in recent years, many have adopted digital subscriber line
as a more marketing-friendly term for the most popular version of consumer-ready
DSL, ADSL.
Typically, the download speed of consumer DSL services ranges from 256 kilobits
per second (kbit/s) to 24,000 kbit/s, depending on DSL technology, line
conditions and service level implemented. Typically, upload speed is lower than
download speed for Asymmetric Digital Subscriber Line (ADSL) and equal to
download speed for Symmetric Digital Subscriber Line (SDSL).
Some variants of DSL connections, like ADSL and very high speed DSL (VDSL),
typically work by dividing the frequencies used in a single phone line into two
primary 'bands'.
The ISP data is carried over the high frequency band (25 kHz
and above) whereas the voice is carried over the lower frequency band (4 kHz and
below). (See the ADSL article on how the high frequency band is sub-divided).
The user typically installs a DSL filter on each phone. This filters out the
high frequencies from the phone, so that the phone only sends or receives the
lower frequencies (the human voice), creating two independent 'bands'. Thus
the DSL modem and the phone can simultaneously use the same phone line without
interfering with each other.
Digital subscriber line technology was originally implemented as part of the ISDN
specification, which is later reused as IDSL. Higher speed DSL connections like HDSL
and SDSL are developed to extend the range of DS1 services on copper lines.
Consumer oriented ADSL is designed to operate also on a BRI ISDN line, which itself
is a form of DSL, as well as on an analog phone line.
DSL, like many other forms of communication, stems directly from Claude
Shannon's seminal 1948 scientific paper describing a theory of digital
communication. Shannon's A Mathematical Theory of Communication laid out the
basic elements of any digital communication:
- An information source which produces a message
- A transmitter which operates on the message to create a signal which can be sent
through a channel
- A channel, which is the medium over which the signal carrying the information that
comprises the message is sent
- A receiver, which transforms the signal back into the message intended for delivery
- A destination, which can be a person or a machine, for whom or which the message
is intended Joe Lechleider at Bellcore (now Telcordia Technologies) developed
ADSL in 1988 by placing wideband digital signals above the existing baseband
analog voice signal carried between telephone company central offices and
customers on conventional twisted pair cabling.
US telephone companies promote DSL to compete with cable modems. DSL service
was first provided over a dedicated "dry loop", but when the FCC required the
incumbent local exchange carriers ILECs to lease their lines to competing
providers such as Earthlink, shared-line DSL became common. Also known as DSL
over UNE), this allows a single pair to carry data (via a digital subscriber
line access multiplexer DSLAM) and analog voice (via a circuit switched
telephone switch) at the same time. In-line low-pass filter/splitters keep the
high frequency DSL signals out of the user's telephones. Although DSL avoids
the voice frequency band, the nonlinear elements in the phone would otherwise
generate audible inter-modulation products and impair the operation of the data
modem.
Older ADSL standards can deliver 8 Mbit/s to the customer over about 2 km (1.25
miles) of unshielded twisted pair copper wire. The latest standard, ADSL2+, can
deliver up to 24 Mbit/s, depending on the distance from the DSLAM. Distances
greater than 2 km (1.25 miles) significantly reduce the bandwidth usable on the
wires, thus reducing the data rate.
Attributes and Credits
The information and facts supplied on this subject
derive from http://en.wikipedia.org/wiki/Main_Page
over the wires of a local telephone network. DSL originally stood for digital
subscriber loop, although in recent years, many have adopted digital subscriber line
as a more marketing-friendly term for the most popular version of consumer-ready
DSL, ADSL.
Typically, the download speed of consumer DSL services ranges from 256 kilobits
per second (kbit/s) to 24,000 kbit/s, depending on DSL technology, line
conditions and service level implemented. Typically, upload speed is lower than
download speed for Asymmetric Digital Subscriber Line (ADSL) and equal to
download speed for Symmetric Digital Subscriber Line (SDSL).
Some variants of DSL connections, like ADSL and very high speed DSL (VDSL),
typically work by dividing the frequencies used in a single phone line into two
primary 'bands'.
The ISP data is carried over the high frequency band (25 kHz
and above) whereas the voice is carried over the lower frequency band (4 kHz and
below). (See the ADSL article on how the high frequency band is sub-divided).
The user typically installs a DSL filter on each phone. This filters out the
high frequencies from the phone, so that the phone only sends or receives the
lower frequencies (the human voice), creating two independent 'bands'. Thus
the DSL modem and the phone can simultaneously use the same phone line without
interfering with each other.
Digital subscriber line technology was originally implemented as part of the ISDN
specification, which is later reused as IDSL. Higher speed DSL connections like HDSL
and SDSL are developed to extend the range of DS1 services on copper lines.
Consumer oriented ADSL is designed to operate also on a BRI ISDN line, which itself
is a form of DSL, as well as on an analog phone line.
DSL, like many other forms of communication, stems directly from Claude
Shannon's seminal 1948 scientific paper describing a theory of digital
communication. Shannon's A Mathematical Theory of Communication laid out the
basic elements of any digital communication:
- An information source which produces a message
- A transmitter which operates on the message to create a signal which can be sent
through a channel
- A channel, which is the medium over which the signal carrying the information that
comprises the message is sent
- A receiver, which transforms the signal back into the message intended for delivery
- A destination, which can be a person or a machine, for whom or which the message
is intended Joe Lechleider at Bellcore (now Telcordia Technologies) developed
ADSL in 1988 by placing wideband digital signals above the existing baseband
analog voice signal carried between telephone company central offices and
customers on conventional twisted pair cabling.
US telephone companies promote DSL to compete with cable modems. DSL service
was first provided over a dedicated "dry loop", but when the FCC required the
incumbent local exchange carriers ILECs to lease their lines to competing
providers such as Earthlink, shared-line DSL became common. Also known as DSL
over UNE), this allows a single pair to carry data (via a digital subscriber
line access multiplexer DSLAM) and analog voice (via a circuit switched
telephone switch) at the same time. In-line low-pass filter/splitters keep the
high frequency DSL signals out of the user's telephones. Although DSL avoids
the voice frequency band, the nonlinear elements in the phone would otherwise
generate audible inter-modulation products and impair the operation of the data
modem.
Older ADSL standards can deliver 8 Mbit/s to the customer over about 2 km (1.25
miles) of unshielded twisted pair copper wire. The latest standard, ADSL2+, can
deliver up to 24 Mbit/s, depending on the distance from the DSLAM. Distances
greater than 2 km (1.25 miles) significantly reduce the bandwidth usable on the
wires, thus reducing the data rate.
Attributes and Credits
The information and facts supplied on this subject
derive from http://en.wikipedia.org/wiki/Main_Page
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