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URL: http://www.dslforum.org/
High Data-Rate Digital Subscriber Line (HDSL) is a
bidirectional and symmetrical transmission system that allows the transport of
signals with a bit rate of 1.544 Mbps or 2.048 Mbps on the copper twisted pairs
of an access network.
The HDSL system uses echo cancellation technique for
the separation of the directions of transmission, so
that one twisted pair can carry both directions. Two different options for the
line code are recommended, the Pulse Amplitude Modulation 2B1Q and the
Carrierless Amplitude/Phase Modulation (CAP). CAP is applicable for 2.048 Mbps
only, while for 2B1Q two different frames for 1.544 Mbps and 2.048 Mbps are
defined. The 2B1Q for 2.048 Mbps caters for both duplex transmission on a
single pair and parallel transmission on two or three-pairs. This allows for
the distribution of the signal to several pairs and for reduction of the symbol
rate and an increase of the line length. CAP is defined for one- or two-pairs
only and the 1.544 Mbps 2B1Q for two-pairs only. HDSL is an ITU-T
recommendation G.991.1
Keywords:
Modem, serial, high speed, physical layer, Access Technology
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