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Very-high-bitrate digital subscriber line (VDSL) is a DSL technology that offers an upstream rate of 12 Mbps and a downstream rate of 52 Mbps. VDSL is considered to be the next-generation DSL that provides a complete package for home communication and entertainment.
VDSL technology is built based on two important technologies: quadrature amplitude modulation (QAM) and discrete multitone modulation (DMT). Of the two, DMT technology is the one most commonly used. The VDSL runs through the copper wires in a telephone line similar to that of an an assymetric digital subscriber line (ADSL) except that it provides much faster transmission speed.
VDSL based on DMT divides the signals into 247 separate virtual channels, each of which is 4 KHz wide. The integrity of each channel is monitored and the data is transferred to an alternate channel when signals become weak. The data is thus continuously switched to the best route, making DMT a robust and complex technology.
Copper lines are increasingly being replaced with fiber optic cable, and many companies are planning on replacing existing copper wires with optic fiber and providing fiber to the curb. Many companies are even planning on fiber to the node, which means installing fiber optic cable to the main junction box for a particular neighborhood instead of drawing cables along each street.