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Chapter 1: Overview
About ADSL
Asymmetric Digital Subscriber Line (ADSL) technology provides high-speed data access across
regular phone lines (copper wires) by making use of previously unused frequency bandwidth
above the voice band. By placing the ADSL signal above the frequency of the voice signal,
ADSL service is able to coexist on the same line with your telephone service. ADSL is
asymmetric in the sense that it provides a higher data rate in the downstream (receive)
direction than in the upstream (transmit) direction. Asymmetric operation is ideal for typical
home and small office use where files and information are downloaded more frequently than
uploaded.
The ADSL USB Modem is capable of supporting the following DSL standards: ANSI T1.413
Issue 2, ITU G.992.1 (G.DMT), ITU G.992.2 (G.lite) and ITU G.992 Annexes A,B and C as
applicable.
Protocol and Device Driver Selection
The ADSL USB Modem can be easily connected to a USB port on the PC via a standard USB
cable. The ADSL USB Modem is fully software upgradeable so that new features and
updates may be added by simply loading a new version of the device driver onto your PC.
ADSL USB modems employ ATM (Asynchronous Transfer Mode) framing. ATM is a protocol
that divides packets into small fixed sized cells for rapid transmission over high-speed
networks. The ATM protocol allows various types of traffic (e.g. data, voice, and video) to be
securely and efficiently carried over the same network. ATM is being widely deployed by
telecommunications carriers in their backbone networks. Two type of ATM connections are
possible, PVC (Permanent Virtual Circuit) and SVC (Switched Virtual Circuit).
Several different protocols are used on top of ATM. The protocol required in your
configuration depends on the equipment deployed by your DSL service provider. There are
several possibilities:
1. Bridged/Routed Ethernet/IP over ATM (RFC 1483) – This protocol makes the modem
appear as a local area network (LAN) device to the operating system.
2. Point to Point Protocol (PPP) Over ATM (RFC 2364) - PPP provides session setup, user
authentication (login), and encapsulation for upper layer protocols such as IP
(Internet Protocol). The use of PPP makes the modem appear as a dial modem to
the operating system. Dial-Up Networking is used to establish a connection.
3.
Point to Point Protocol (PPP) Over Ethernet (RFC 2516) - PPPoE combines the
Point-to-Point Protocol commonly used in dialup connections, with the Ethernet
protocol, which supports multiple users in a local area network. The PPP Protocol
information is encapsulated within an Ethernet frame. The use of PPP makes the
modem appear as a dial modem to the operating system. Dial-Up Networking is used
to establish a connection.
