VDSL
VDSL is high-speed form of DSL, "very high bitrate DSL". Compare HDSL (High Bitrate Digital Subscriber Line).
Currently, the standard VDSL uses up to 4 different frequency bands, two for upstream (from the telco to the client) 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 available bit rates ranges from about 26Mbps symmetric for a loop of about 1500 m, up to 100 Mbps symmetric for a few hundred metres.
As of 2003, the market is still small, most of it in Korea. In the US, Qwest is offering both internet and television services over VDSL in the following markets:
The current mostly used technology is QAM (the same technology used in cable modems).
