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VDSL Systems

As more people buy home computers and create home networks, the demand for broadband (high-speed) connections steadily increases. Asymmetric Digital Subscriber Line (ADSL) technology currently dominate the industry.

While this technology provides Internet connections that are many times faster than a 56K modem, it still is not fast enough to support the integration of home services such as digital television and video-on-demand.

Standard phone service limits the frequencies that the switches, telephones and other equipment can carry, however, human voice, speaking in normal conversational tones, can be carried in a frequency range of 400 to 3,400 Hertz (cycles per second) and, in most cases, the wires themselves have the potential to handle frequencies of up to several-million Hertz.

Modern equipment that sends digital data can safely use much more of the telephone line’s capacity, and DSL does just that.

VDSL or VHDSL (Very-high-bit-rate Digital Subscriber Line) is a DSL (Digital Subscriber Line) technology providing faster data transmission over a single untwisted or twisted pair of copper wires.

These fast speeds mean that VDSL is capable of supporting high bandwidth applications such as HDTV, as well as telephone services (Voice over IP) and general Internet access, over a single connection.

VDSL is deployed over existing wiring used for POTS (Plain Old Telephone Service) and lower-speed DSL connections.

Second-generation of VDSL systems, the VDSL2, use bandwidth of up to 30 MHz to provide data rates exceeding 100 Mbit/s simultaneously in both the upstream and downstream directions. The maximum available bit rate is achieved at a range of about 300 meters; performance degrades as the loop attenuation increases.

Currently, the standard VDSL uses up to 7 different frequency bands, which enables customization of data rate between upstream and downstream depending on the service offering and spectrum regulations.

First generation VDSL standard specified both QAM (Quadrature amplitude modulation) and DMT (Discrete Multi-Tone modulation). In 2006, ITU-T standardized VDSL in recommendation G.993.2 which specified only DMT modulation for VDSL2.

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