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VDSL (very high bit-rate DSL (DSL) is an xDSL technology providing data transmission up to a theoretical limit of 52 Mbit/s downstream and 12 Mbit/s upstream over a single twisted pair of wires. Compare HDSL (High bit-rate Digital Subscriber Line).
Currently, the standard VDSL uses up to 4 different frequency bands, two for upstream (from the client to the telco) and two for downstream.
The standard modulation technique is either QAM (Quadrature amplitude modulation) or DMT (Discrete multitone modulation) which are not compatible, but have similar performance. The current mostly used technology is QAM (the same technology used in cable modems).
The available bit rates ranges from about 26 Mbit/s symmetric for a loop of about 1500 m, up to 100 Mbit/s symmetric for a few hundred metres.
VDSL is capable of supporting high bandwidth applications such as HDTV. Qwest is currently prototyping the service and may offer a HDTV package as early as 1Q 05.
Supply
As of 2004, the market is still small, except in South Korea, which is the only place that VDSL is taking the majority.
- Australia
- The sole VDSL supplier is TransACT, who use VDSL for Digital TV, Internet and WAN applications over their Fibre-To-The-Curb network. (VDSL is not ratified for use on Telstra supplied copper lines in Australia yet, and Telstra has publically voiced opposition (http://whirlpool.net.au/article-past.cfm?q=VDSL) to VDSL).
- Belgium
- Belgacom is providing VDSL in parts of Gent, Brussels, Liege and Mons (about 3% coverage), but limited to 9 Mbps down, 400 Kbps up and with a monthly download limit of 15 GiB.
- South Korea
- VDSL is offered in urban areas by several providers, costing about $20-$30 USD/month.
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