Adsl Overview - Huawei AR1200 series Configuration Manual

Huawei AR1200 Series Enterprise Routers
Configuration Guide - Interface Management

12.1 ADSL Overview

Asymmetric Digital Subscriber Line (ADSL) is a data communications technology that enables
fast data transmission over copper twisted pairs by employing high frequencies that are not used
by regular telephone lines.
Background
Depending on transmission media, network access modes include wired access, wireless access,
and combination of wired and wireless access. Wired access includes twisted pair access, fiber
access, and access by using both twisted pairs and fibers. Traditional copper twisted pairs are
widely used for access, so ADSL becomes the most competitive access mode.
ADSL uses the frequency division multiplexing (FDM) technology to classify telephone lines
into regular telephone lines, upstream channels, and downstream channels, avoiding
interference. ADSL can provide channelized data services (including E1/Tl, FR, IP, and ATM
services) and transmit data, voice, and video signals at a high rate.
ADSL Evolution
The first ADSL standards (G.992.1 G.DMT and G.992.2 G.Lite) supported the upstream
transmission rate of 640 kbit/s to 2 Mbit/s, downstream transmission rate of 1 Mbit/s to 8 Mbit/
s, and transmission distance of 3 to 5 km. Since the release of ADSL in June 1999, the ITU has
been improving the ADSL transmission performance, anti-attenuation and anti-interference
capabilities, line diagnosis, and operation maintenance. In 2002, the ITU released ADSL2, which
comprises two new ADSL standards (G.992.3 and G.992.4). In 2003, the ITU defined G.992.5,
which is referred to as ADSL2+.
Compared with the first ADSL technology, ADSL2/2+ has the following advantages:
1.
2.
3.
ADSL System
As shown in
Multiplexer (DSLAM) and Customer Premises Equipment (CPE).
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Issue 01 (2012-04-20)
ADSL2 improves performance in long-distance transmission, anti-attenuation, and anti-
noise. ADSL2 also improves the frame structure, so it can provide a maximum of 1 Mbit/
s upstream transmission rate and 12 Mbit/s downstream transmission rate. Expanding the
frequency spectrum used, ADSL2+ greatly improves transmission performance and
provides a maximum rate of 1 Mbit/s upstream and 24 Mbit/s downstream.
In addition to providing higher rates, ADSL2/2+ improves transmission performance in
long-distance transmission and anti-interference by improving the modulation rate and
coding gain, reducing the frame overhead, and using enhanced signal processing methods.
Currently, ADSL provides a transmission distance of 3 km, whereas ADSL2+ achieves a
maximum of 6 km transmission distance.
ADSL2/2+ saves energy. The first ADSL technology provides the same transmission rate
regardless of whether data is being transmitted. ADSL2/2+ enables a transmitter to enter
the sleep state when the data transmission rate is low or no data is being transmitted,
reducing power consumption and heat dissipation.
Figure 12-1, an ADSL system consists of a Digital Subscriber Line Access
A DSLAM is an aggregation device that terminates ADSL packets on the central office.
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