Very-high-speed digital subscriber line(VDSL) is the fastest access technology of the xDSL family.The new VDSL system’s bandwidth can reach 100 Mbit/s on a single telephone wire pair.It can provide very high symmetric and asymmetric bandwidth.Because of the high rate
the transmission distance of the VDSL is shorter than the other DSL technology.The mode of the modulation is the key technique. At present
There are two different modulation mode(DMT and QAM/CAP mode).This article explains the two modulation modes
and compare the excellence and the disadvantage of these modes.