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About ADSL F-1
The Netopia R6000 Series ADSL Router (Asymmetric 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. ADSL allows a much faster data connection. The ADSL Router
provides the bandwidth needed for business applications such as e-mail, file transfer, Web browsing, corporate
Intranet access, Web hosting, and remote LAN access. The ADSL Router improves businesses productivity and
competitiveness by providing cost-effective, high-speed Internet access over ordinary copper phone lines. ADSL
creates a point-to-point link over a single copper wire so bandwidth isn't shared by anyone outside the remote
office.
ADSL is a broadband communication technology designed for use on regular telephone lines. ADSL splits the
telephone line into two frequency ranges. The frequencies below 4 kHz are reserved for voice, and the range
above that is used for data. This makes it possible to use the telephone line for telephone calls and data
network access at the same time.
The voice channel can be either a Plain Old Telephone Service (POTS) or Integrated Services Digital Network
(ISDN). The former is most commonly deployed in North America, whereas the latter is most common in
Europe. The voice channel is split off from the data channel by filters, thereby guaranteeing uninterrupted
POTS/ISDN service even if the ADSL service fails.
In order to use the frequencies above the voice audio spectrum, ADSL equipment must be installed on both
ends and the copper wire in between must be able to sustain the higher frequencies for the entire route. This
means that bandwidth limiting devices such as loading coils must be removed or avoided.
ADSL is "asymmetric" because more bandwidth is reserved for receiving data than for sending data. The
asymmetric nature of ADSL is useful because typical Internet applications such as Web browsing involve
receiving much more data than is sent. Download ("downstream") speeds range from 256 Kilobits per second
up to 6 Megabits per second (optionally 8 Megabits per second), and upload ("upstream") speeds range from
16 to 640 Kilobits per second (optionally 1 Megabit per second).
Although there are two competing line coding techniques for modulating ADSL signals on twisted-pair copper
wiring — Carrierless Amplitude and Phase (CAP) and Discrete MultiTone (DMT) — the latter is the basis for the
ANSI and ETSI ADSL standards. Two different forms of DMT-based ADSL, known as G.dmt (or full-rate ADSL)
and G.lite (or ADSL lite), have been standardized.
G.dmt can deliver up to 8 Megabits per second downstream and up to 1 Megabit per second upstream. G.lite
can deliver up to 1.5 Mbps downstream and up to 512 Kbps upstream. G.lite operates at lower frequencies
that G.dmt, which allows it to transmit data over longer distances — up to 18,000 feet between the customer's
premises and the central office. G.dmt requires installation of a device known as a splitter on the telephone
line where it enters the home or business in order to separate the voice service from the data service. G.lite is
sometimes referred to as "Splitterless" ADSL, which is somewhat of a misnomer. G.lite eliminates the splitter
at the entry to the customer premises, and instead uses a distributed splitter approach consisting of low-pass
filters (LPFs or microfilters) located at each telephone in the customer premises, and a high-pass filter (HPF)
built-in to the ADSL modem.
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