The line-length limitations from telephone exchange to subscriber impose more restrictions on higher data-transmission rates. Technologies such as VDSL provide very high speed, short-range links as a method of delivering "triple play" services (typically implemented in fiber to the curb network architectures). Technologies like GDSL can further increase the data rate of DSL. Fiber Optic technologies exist today that allow the conversion of copper based ISDN, ADSL and DSL over fiber optics.
DSL technologies (sometimes summarized as xDSL) include:
- ISDN Digital Subscriber Line (IDSL), uses ISDN based technology to provide data flow that is slightly higher than dual channel ISDN.
- High Data Rate Digital Subscriber Line (HDSL / HDSL2), was the first DSL technology that used a higher frequency spectrum of copper, twisted pair cables.
- Symmetric Digital Subscriber Line (SDSL / SHDSL), the volume of data flow is equal in both directions.
- Symmetric High-speed Digital Subscriber Line (G.SHDSL), a standardized replacement for early proprietary SDSL.
- Asymmetric Digital Subscriber Line (ADSL), the volume of data flow is greater in one direction than the other.
- Asymmetric Digital Subscriber Line 2 (ADSL2), an improved version of ADSL
- Asymmetric Digital Subscriber Line 2 Plus (ADSL2+), A version of ADSL2 that doubles the data rates by using twice the spectrum.
- Asymmetric Digital Subscriber Line Plus Plus (ADSL++), technology developed by Centillium Communications (Centillium has been acquired by TranSwitch Corp.) for the Japanese market that extends downstream rates to 50 Mbit/s by using spectrum up to 3.75 MHz.
- Bonded DSL Rings (DSL Rings), A shared ring topology at 400 Mbit/s
- Rate-Adaptive Digital Subscriber Line (RADSL), designed to increase range and noise tolerance by sacrificing up stream speed
- Very High Speed Digital Subscriber Line (VDSL)
- Very High Speed Digital Subscriber Line 2 (VDSL2), an improved version of VDSL
- Etherloop Ethernet Local Loop
- (Extended-) Reach Digital Subscriber Line
- Uni-DSL (Uni Digital Subscriber Line or UDSL), technology developed by Texas Instruments, backwards compatible with all DMT standards
- Gigabit Digital Subscriber Line (GDSL), based on binder MIMO technologies.
- Universal High bit rate Digital Subscriber Line (UHDSL) using fiber optics. Developed in 2005 by RLH Industries, Inc. Converts HDSL-1, 2 or 4 copper service into fiber optic HDSL service.
- Internet Protocol Subscriber Line (IPSL), developed by Rim Semiconductor in 2007, allowed for 40 Mbit/s using 26 AWG copper telephone wire at a 5,500 ft (1,700 m) radius, 26 Mbit/s at a 6,000 ft (1,800 m) radius. The company operated until 2008.
Read more about this topic: Very High Speed ADSL
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