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Digital Subscriber Line (DSL) is a popular Internet access technology, currently competing with Cable TV Internet for supremacy. DSL allows for high-speed data connections over standard copper phone lines (identical to those used for traditional local telephone service.) For a DSL connection to function, the customer must be located less than 550 m (1800 feet; by cable length) from a Central Office. It is important that the line be in good condition, and that no filters be present, as DSL utilizes non-voice-band frequencies. Various types of DSL exist, including ADSL (Asymmetric Digital Subscriber Line) and SDSL? (single-pair Symmetric Digital Subscriber Line), and HDSL (High Bit Rate Digital Subscriber Line). ADSL, which provides a higher downlink bandwidth than uplink bandwidth, is the most common type of DSL. Many ADSL subscribers are actually receiving HDSL, because many of the larger phone service providers had this type of technology already installed in their Central Offices. The end user never really knows that it's HDSL, because the multiplexers and other network equipment is set to mimic a "normal" ADSL signal. Recently, DSL has been the most common type of [broadband connection]? available, due to the relative ease with which it can be rolled out to individual customers using existing infrastructure. However, the rapid consumption of free copper pairs is limiting its future potential in some areas. Moreover, DSL can only be provided within certain distances: ADSL has a limit of about 3700 m (12,000 feet); SDSL to 4900-5200 m (16-17,000 feet), and IDSL (DSL supplied over an ISDN pair) a bit further. Some of the common "DSL Killers" are: * [Bridged taps]? * [Load coils]? * "SLIC" boxes, or splitters, where copper capacity is increased by extending with multiple fibres. DSL can't travel over fibre, and most telephone companies choose not to offer fibre connections to residential customers. * "DACS" boxes, where two baseband analog telephone lines are multiplexed over a single copper pair using ISDN-like technology to connect to the central office. Neither of the multiplexed lines is then usable for either DSL or ISDN service, as there is no metallic high-frequency path available. Where the central office connection is demultiplexed to analog connections, there is the added disadvantage that standard analog modem speeds are also reduced significantly. Many DSL technologies implement an ATM layer over the low-level bitstream layer to enable the adaptation of a number of different technologies over the same link. See also: * modem * COFDM |
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Digital Subscriber Line (DSL) refers to a family of technologies that provide a digital connection to the telephone network. It is currently the principle competitor to Cable Modems to provide high speed Internet access to the home consumer. DSL is provided over the standard copper phone lines that provide the majority of traditionaltelephone service. Many DSL's can run in conjunction normal POTS service by utilising splitters and using non-voice-band frequencies. Example DSL technologies (sometimes called xDSL) include: * ISDN (pre-dates the use of the term DSL) * IDSL? (ISDN Digital Subscribe Line, a data-only ISDN variant) * HDSL? (High Bit Rate Digital Subscriber Line) * ADSL (Asymmetric Digital Subscriber Line) * SDSL? (Symmetric Digital Subscriber Line, a standardised version of HDSL) * VDSL? (Very high speed Digitial Subscriber Line) The reach restraints (line length from Central Office to Subscriber) reduce as the data rates increase, with technologies like VDSL being used for short range links (typically "Fibre to the Curb" network scenarios). Many DSL technologies implement an ATM layer over the low-level bitstream layer to enable the adaptation of a number of different technologies over the same link. See also: * modem * COFDM /Talk |
Example DSL technologies (sometimes called xDSL) include:
The reach restraints (line length from Central Office to Subscriber) reduce as the data rates increase, with technologies like VDSL being used for short range links (typically "Fibre to the Curb" network scenarios).
Many DSL technologies implement an ATM layer over the low-level bitstream layer to enable the adaptation of a number of different technologies over the same link.
See also:
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