ADSL vs VDSL
This page on ADSL vs VDSL describes difference between ADSL and VDSL .
ADSL stands for Asynchronous Digital Subscriber line. This system provides 8Mbps data rate in the downstream while 640kbps rate in the upstream over standard telephone lines. Here term Asynchronous refers to unequal data rates in the downstream and in the upstream.
Modulation scheme used in ADSL is DMT(Discrete Multitone). This divides upper part of frequency spectrum into 256 channels. Each of these channels are 4KHz wide. Each of this channels carry about 60kbps and referred as bin. Upstream uses spectrum from 25.875KHz to 138.8KHz,bins are about 4KHz wide here too. As mentioned downstream bins will occupy frequency spectrum from 138KHz to about 1.1 MHz. QAM technique is used to map more than one bits on to each carrier.
Several versions are available for ADSL modem based on data rate depending upon length of the subscriber twisted pair.
VDSL stands for very high bit rate digital subscriber line. It is the next generation of modem technology. It provides faster data rate compare to ADSL modem technology over coper wires or coaxial cables. This made VDSL modem popular for use in digital TV,VOIP and even for internet applications.
ADSL over twisted pair of copper provides data rate of about 52Mbps in the downstream and 16Mbps in the upstream. ADSL over coaxial cable provides about 80 Mbps of data rate in both the downstream as well as upstream.
ITU G.993.1 and ITU G.993.2 are the standards to be followed for VDSL. It uses QAM and DMT modulation techniques.
Article on ADSL Basics
This page describes ADSL system basics overview, typical ADSL setup, ADSL types and ADSL standards. It covers IDSL, HDSL, SHDSL, RADSL, UDSL, VDSL, GDSL etc., READ MORE>>
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