Netopia 4752 - Manual (Page 243)

About SDSL B-1
A A A Ap p p pp p p pee e en n n nd d d diiiixxxx B B B B
A A A Ab b b bo o o ou u u utttt S S S SD D D DS S S SLLL L
The Netopia 4752 SDSL Integrated Access Device (Symmetric Digital Subscriber Line) technology uses
standard copper phone lines to send a digital signal between two points. Because the signal stays digital and
does not go through the public switched telephone network SDSL allows a much faster data connection.
Offering the same data rate in both directions, the SDSL Router provides symmetric bandwidth needed for
business applications such as e-mail, file transfer, web browsing, corporate Intranet access, web hosting, and
remote LAN access. The SDSL Router improves businesses productivity and competitiveness by providing cost
effective, high speed Internet access over ordinar y copper phone lines. SDSL creates a point-to-point link over
a single copper wire so bandwidth isn't shared by anyone outside the remote office.
SDSL will allow you to connect to the Internet at a minimum of 128Kbps bi-directional, up to 1.568Mbps. Your
LAN will constantly be connected and you will not have to dial into the Internet. DSL utilizes more of the
bandwidth on copper phone lines than what is currently used for plain old telephone ser vice (POTS). By utilizing
frequencies between 26 kHz and 1MHz, DSL can encode more data to achieve higher data rates than would
other wise be possible in the restricted frequency range of a POTS network (up to 4 kHz). In order to utilize 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.
SDSL is more appropriate for business users because bandwidth is the same in both directions. Asymmetric
DSL Ser vice is better suited for individual consumers who generally require more speed in the download stream
(web sur fing) with little data going in the other direction.
Netopia's SDSL router has fewer implementation issues than ADSL routers. It uses 2B1Q line encoding (same
as T1 or ISDN) and this doesn't produce the same noise and inter ference as ADSL, which uses DMT or CAP
encoding. In some cases the phone company may refuse to provision ADSL ser vice due to crosstalk with other
voice and data lines bundled in the same cable.
Historically, HDSL has been primarily used to deploy repeaterless T1 and E1 ser vices 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., SDSL) but still delivers up to 2 Mbps of symmetrical bandwidth depending on loop
length and quality.
Single pair HDSL (S-HDSL or SDSL) offers workable solutions to several of the challenges faced today by its
less mature cousin, ADSL. Both technologies will have their place in the ser vice provider's network, and that
will be based on the specific customer applications that are suppor ted over the last mile connection. However,
SDSL offers some ver y attractive solutions to today's main drivers—remote data connectivity for corporate or
Internet applications.
Because SDSL uses the same technology as the market-proven HDSL, it benefits from the maturity of HDSL
implementations. For example, SDSL silicon chipsets cost about a third of that for ADSL chipsets. The lower per
line cost means ser vice providers can launch high speed data ser vices sooner rather than later.
Higher speed ADSL solutions can then be brought on line when they are more cost effective.
The maturity of SDSL silicon also includes an advantage in the area of power consumption. Where most ADSL
implementations require 6-8 watts of power, current SDSL modems consume 4 watts of power or less.