ADSL loop extender
A DSL loop extender or DSL repeater is a device that a telephone company can place midway between the subscriber and central office to extend the distance and increase the channel capacity of a DSL connection. ADSL repeaters are aggressively deployed by rural telephone companies trying to provide rural Internet service to farms and small towns where it is impractical to place the DSLAM closer.[1]
Multiple loop extenders can be placed on a line, making the reach of ADSL effectively infinite. Therefore, any subscriber can get any ADSL speed using multiple loop extenders.
A repeater can either be an amplifier or a re-generator. Amplifiers increase the signal level of the analog transmission signal, whereas 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) that have no distance limits. Because of the simplicity of the amplifier circuits, amplifiers cost less 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 used. An ADSL loop extender works as an amplifier, boosting the signal level so it can travel longer distances. In some cases, service can be established as far as 10 miles from the Central Office.
In 2006, the US telecommunications industry promoted Fiber to the Home. 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.[2] With most of the "brownfield" market already tapped for ADSL,[3] Telcos finally are interested in extending ADSL to those semi-rural areas that have never been important before.[4]
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 [5]. 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 not repeaters, but instead convert to a different signal (like G.shdsl) whose range can be extended with repeaters. If additional amplification in the C.O. were a good idea, the DSLAM and modem makers would simply transmit signals with a higher power. However, additional amplification creates crosstalk and is not compliant with T1.417 spectrum management.[6] 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.
References
- ^ Strowger :: Infinite Reach ADSL
- ^ Light Reading - Broadband - Carrier Scorecard: Economic Uncertainty - Telecom News Analysis
- ^ Light Reading - Broadband - US Broadband Growth Slows - Telecom News Analysis
- ^ NewPA.com : Press Releases
- ^ Connect America Fund
- ^ Broadband last mile: access technologies for multimedia communications By Nikil Jayant p339, Google Books