Atec JDSU-SC-ADSL - Manual (Page 2)

COMMUNICATIONS TEST & MEASUREMENT SOLUTIONS
ADSL2+ has emerged as an IPTV-enabling technology of choice for network
operators and services providers seeking new revenue streams and competitive
positioning. At the same time consumers are signing up for multiple services in
this very competitive environment expecting the best service quality, making it
imperative that operators quickly and cost-effectively install ADSL2+ lines with
the confidence that their complex triple-play services are working well.
Delivery of ADSL services requires a single copper pair configuration of a
standard voice circuit with an ADSL modem at each end of the line, creating three
information channels — a high-speed downstream channel, a medium-speed
upstream channel, and a plain old telephone service (POTS) channel for voice.
Data rates depend on several factors including the length of the copper wire, the
wire gauge, presence of bridged taps, and cross-coupled interference. The line
performance increases as the line length is reduced, wire gauge increases, bridged
taps are eliminated and cross-coupled interference is reduced or is canceled out by
a good longitudinal balance characteristic of the copper wire. The modem located
at the subscriber’s premises is called an ADSL transceiver unit-remote (ATU-R),
and the modem at the central office is called an ADSL transceiver unit-central
office (ATU-C). The ATU-Cs take the form of circuit cards mounted in the digital
subscriber line access multiplexer (DSLAM), while a residential or business
subscriber connects their PC and ATU-R modem to a telephone outlet on
the wall.
ADSL2 has been specifically designed to improve the rate and reach of ADSL
largely by achieving better performance on long lines. ADSL2 accomplishes this
by improving modulation efficiency, reducing framing overhead, achieving higher
coding gain, improving the initialization state machine, and providing enhanced
signal processing algorithms. ADSL2+ further improves on the ADSL2 standard
by allocating additional spectrum for downstream data, dramatically improving
the data rate over ADSL2 or ADSL.
2
ADSL and IPTV Overview