Very-high-bitrate digital subscriber line

Very-high-bitrate DSL (VDSL or VHDSL) is a DSL technology providing faster data transmission (up to 52 Mbit/s downstream and 16 Mbit/s upstream) over a single flat 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 and lower-speed DSL connections. This standard was approved by ITU in November 2001.

Second-generation systems (VDSL2; ITU-T G.993.2 approved in February 2006) utilize frequencies 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 quadrature amplitude modulation (QAM) and discrete multi-tone modulation(DMT). In 2006, ITU-T standardized VDSL in recommendation G.993.2 which specified only DMT modulation for VDSL2.

Very-high-speed digital subscriber line 2 (VDSL2) is an access technology that exploits the existing infrastructure of copper wires that were originally deployed forPOTS. It can be deployed from central offices, from fibre-fed cabinets located near the customer premises, or within buildings.

VDSL2 is the newest and most advanced standard of DSL broadband wireline communications. Designed to support the wide deployment of triple play services such as voice, video, data, high definition television (HDTV) and interactive gaming, VDSL2 is purported to enable operators and carriers to gradually, flexibly, and cost-efficiently upgrade existing xDSL infrastructure.

The protocol was standardized as ITU G.993.2 on February 17, 2006.

ITU-T G.993.2 (VDSL2) is an enhancement to G.993.1 (VDSL) that permits the transmission of asymmetric and symmetric aggregate data rates up to 200 Mbit/s downstream and upstream on twisted pairs using a bandwidth up to 30 MHz.

VDSL2 deteriorates quickly from a theoretical maximum of 250 Mbit/s at source to 100 Mbit/s at 0.5 km (1,600 ft) and 50 Mbit/s at 1 km (3,300 ft), but degrades at a much slower rate from there, and still outperforms VDSL. Starting from 1.6 km (1 mi) its performance is equal to ADSL2+.

ADSL-like long reach performance is one of the key advantages of VDSL2. LR-VDSL2 enabled systems are capable of supporting speeds of around 1–4 Mbit/s (downstream) over distances of 4–5 km (2.5–3 miles), gradually increasing the bit rate up to symmetric 100 Mbit/s as loop-length shortens. This means that VDSL2-based systems, unlike VDSL1 systems, are not limited to short local loops or MTU/MDUs only, but can also be used for medium range applications.

Source : wikipedia

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