ADSL loop extender
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A DSL loop extender is a device that a
telephone company A telephone company, also known as a telco, telephone service provider, or telecommunications operator, is a kind of communications service provider (CSP), more precisely a telecommunications service provider (TSP), that provides telecommunicat ...
can place between subscriber premises equipment and central office interfaces to extend the distance and increase the channel capacity of
digital subscriber line Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric di ...
(DSL) connections. ADSL repeaters are deployed by rural telephone companies trying to provide
rural Internet Rural Internet describes the characteristics of Internet service in rural areas (also referred to as "the country" or "countryside"), which are settled places outside towns and cities. Inhabitants live in villages, hamlets, on farms and in other ...
service to farms and small towns where it is impractical to place the
DSLAM A digital subscriber line access multiplexer (DSLAM, often pronounced ''DEE-slam'') is a network device, often located in telephone exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital co ...
closer to the subscriber. Typical distance improvements with a loop extender are shown in the diagram below, with rate in megabits per second and distance in thousands of feet. Multiple loop extenders can be placed on a line, effectively making the reach of the ADSL signal infinite. That is, it is possible to reach any subscriber with any ADSL speed if one uses multiple loop extenders. A
repeater In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Some ...
can either be an amplifier or a re-generator. Amplifiers increase the signal level of the analog transmission signal; re-generators demodulate the signal to binary, then re-modulate it into the original transmission frequency. Because regeneration restores the signal to binary, an indefinite number of re-generators can be placed on a line and is the preferred choice for services like T1 (
Digital Signal 1 Digital Signal 1 (DS1, sometimes DS-1) is a T-carrier signaling scheme devised by Bell Labs. DS1 is the primary digital telephone standard used in the United States, Canada and Japan and is able to transmit up to 24 multiplexed voice and data cal ...
) that have no distance limits. Because of the simplicity of the amplifier circuits, amplifiers are of lower cost than re-generators. Before the development of ADSL loop extenders and remote DSLAMs, ADSL was limited to 3–6 miles (5–10 km) from the Central Office depending on the
wire gauge Wire gauge is a measurement of wire diameter. This determines the amount of electric current the wire can safely carry, as well as its electrical resistance and weight. Types of wire gauge Wire gauges may be broadly divided into two groups, th ...
used. An ADSL Loop Extender works as an amplifier, boosting the signal level so it can travel longer distances. In some cases, service can now be established as far as 10 miles from the Central Office. In 2006, US telco promoted
Fiber to the Home Fiber to the ''x'' (FTTX; also spelled "fibre") or fiber in the loop is a generic term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last mile telecommunications. As fiber opt ...
. This was driven by a rapidly growing housing sector that was creating the " greenfield" customers that are needed to make fiber to the home profitable. Later, with the housing sector in a serious recession, that "greenfield" seems to be drying up fast. With most of the "
brownfield In urban planning, brownfield land is any previously developed land that is not currently in use. It may be potentially contaminated, but this is not required for the area to be considered brownfield. The term is also used to describe land prev ...
" market already tapped for ADSL, Telcos finally are interested in extending ADSL to those semi-rural areas that have never been important before. In 2010, the US Federal Government updated the subsidies paid to rural telephone companies so that broadband is subsidized rather than phone service in a program called Connect America Fund. In order to qualify for subsidy, the telephone company must provide 4 mbits downstream and 1 mbit upstream. This has increased the demand for ADSL loop extenders because loop extenders will allow the telephone companies to reach the most distant subscribers in a way that is more cost effective than deploying remote DSLAMs. Some ADSL loop extenders aren't repeaters, but instead convert to a different signal (like G.shdsl) that fares better over extreme distances. This is because G.shdsl can use the lower frequencies that ADSL reserved for voice use.
Crosstalk In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, induc ...
has been analyzed using T1.417 Method B and found to be compliant. Since the objective is to provide DSL to locations where no other data service can reach, or is needed (e.g. onto a farm), and ordinary telephone service is very immune to cross talk from ADSL due to ADSL not using voice frequency range, the cross talk issue is further reduced. Converting to G.shdsl or other technologies has problems too. These technologies have limited downstream speed, thus are less useful except to extend services to the most distant customers. Their many components (special C.O., re-generators, CPE) make them more expensive than ADSL amplifiers.


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List of public service commissions
{{DEFAULTSORT:Adsl Loop Extender Digital subscriber line Telecommunications equipment Communication circuits