PairGain 500L, User Manual

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Megabit Modem 500L Installation Manual 55
PR
EL
IM
IN
A
RY
9
T
ECHNICAL
R
EFERENCE
This chapter provides technical information about how your modem transmits data between
users on your LAN and a service provider over the WAN.
T
RANSMISSION ON THE
W
IDE
A
REA
N
ETWORK
The technology is ATM over DMT ADSL that provides the high-speed transmission between
the modem and the service provider. This transmission occurs over a single-pair telephone line.
The following sections describe these technologies.
ADSL
Asymmetric Digital Subscriber Line (ADSL) is the technology used to transmit data between
the modem and service provider at the physical layer. It provides data at asymmetric rates so
that downstream traffic from a service provider to you is faster than upstream traffic from you
to the service provider. The downstream transmission rate is up to 7.552 Mbps, while the
upstream rate is up to 928 kbps. Analog POTS can coexist with ADSL on the same line.
Discrete Multitone (DMT) is the line coding used for ADSL. Basically, it divides the
bandwidth into subchannels. Some of the subchannels are reserved for analog POTS. The
other subchannels are allocated to upstream and downstream traffic. Within the upstream
and downstream subchannels, some subchannels are used for management and
performance functions.
DMT ADSL provides rate-adaptive transmission that allows the service provider to deliver you
the best transmission rate determined by distance and line conditions.