Netopia R6100 Reference Manual page 336

F-2 User's Reference Guide
Like all flavors of DSL, ADSL is distance sensitive. As the distance between the customer premises and the
central office increases, the available bandwidth decreases:
Connection speeds for DSL typically range from 384 Kbps to 1.544 Mbps downstream and 128 Kbps
upstream. Your LAN will constantly be connected and you will not have to dial into the Internet. DSL uses more
of the bandwidth on copper phone lines than what is currently used for plain old telephone service (POTS). By
using frequencies between 26 kHz and 1 MHz, DSL can encode more data to achieve higher data rates than
would otherwise be possible in the restricted frequency range of a POTS network (up to 4 kHz). In order to use
the frequencies above the voice audio spectrum, DSL equipment must be installed on both ends and the
copper wire in between must be clean enough to sustain the higher frequencies for the entire route. This means
that bandwidth limiting devices such as loading coils can prevent DSL from being used.
Historically, HDSL has been primarily used to deploy repeaterless T1 and E1 services in areas where repeater
installation was costly or problematic. Today there are over 300,000 such lines installed in the U.S. While these
implementations typically require two or three pairs of copper wire, a new form of HDSL has emerged that uses
a single pair of copper (i.e., ADSL) but still delivers up to 2 Mbps of bandwidth depending on loop length and
quality.
Single pair HDSL (S-HDSL or ADSL) offers workable solutions to several of the challenges faced today by its
less mature cousin, ADSL. Both technologies will have their place in the service provider's network, and that
will be based on the specific customer applications that are supported over the last mile connection. However,
ADSL offers some very attractive solutions to today's main drivers—remote data connectivity for corporate or
Internet applications.
Because ADSL uses the same technology as the market-proven HDSL, it benefits from the maturity of HDSL
implementations. For example, ADSL silicon chipsets cost about a third of that for ADSL chipsets. The lower per
line cost means service providers can launch high speed data services sooner rather than later.
Higher speed ADSL solutions can then be brought on line when they are more cost effective.
The maturity of ADSL silicon also includes an advantage in the area of power consumption. Where most ADSL
implementations require 6-8 watts of power, current ADSL modems consume 4 watts of power or less.
Because over 300,000 lines are already deployed using HDSL, service providers feel comfortable with ADSL
since it uses the same technology as its predecessor and ISDN. The line coding employed by both HDSL and
ISDN has not caused any interference with existing services like T1. This means service providers deploy ADSL
solutions without worry about impact on other services in neighboring binder groups.
Distance from
Central Office
8,000 feet
12,000 feet
16,000 feet
20,000 feet
Maximum
Downstream Speed
8 Mbps
6 Mbps
2 Mbps
1.5 Mbps