I
NTRODUCTION

1-4

Networking Concepts

ADSL

Digital Subscriber Line (DSL) technology transmits both data and voice
over ordinary telephone lines. Signals above 4 kHz are cut off in normal
telephone communications as noise, so DSL uses this spectrum to
transmit data.
Since Internet users and people telecommuting from home normally
download more data than they upload, Asymmetric Digital Subscriber Line
(ADSL) is the preferred choice. Full-rate ADSL utilizes Discrete
Multi-Tone (DMT) signaling to transmit data at up to 8 Mbps downstream
and 640 Kbps upstream. While the more economical splitterless G.lite
connection transmits data at up to 1.5 Mbps downstream and 512 Kbps
upstream.
Because the ADSL signal path is always on, you no longer have to wait
each time you want to access the Internet or a remote site. Moreover, with
multiprotocol encapsulation that includes TCP/IP, NetWare IPX, and
Windows NetBEUI, you have instant access to the Internet, as well as all
the networked resources at your office, including file servers, printers, or
multimedia services. The ADSL Router makes telecommuting a real
possibility for the first time.

ATM

This router uses Asynchronous Transfer Mode (ATM) over ADSL since
ATM permits the concurrent transmission of data, voice, and video. ATM
is a transport mechanism that configures a network connection between
two nodes as a Virtual Path (VP) running across a series of routers or
Layer-3 switches. A Virtual Path can contain many different Virtual
Circuits (VC), each of which is set up to transport a unique data flow
between the source and destination node.