Introduction
Digital Subscriber Line (DSL) is a copper access technology that transmits digital signals over regular telephone wires. It has become very popular in the US and is relatively cheap and fast (greater than 128Kbps).

There are many variations to the xDSL technology:

1. Digital Subscriber Line (DSL)
2. High Data Rate Digital Subscriber Line (HDSL)
3. Very High Data Rate Digital Subscriber Line (VHDSL)
4. Asymmetric Digital Subscriber Line (ADSL)

ADSL (Asymmetric Digital Subscriber Line) is a technology for transmitting digital information at high bandwidths on existing telephone lines to homes and businesses.

ADSL is asymmetric in that it uses most of the channel to transmit downstream to the user and only a small part to receive information from the user.

ADSL supports speeds of 1.5 to 8Mbps depending on line quality and distance. Upstream rates range between 16 and 640Kbps, again depending on line quality and distance.

ADSL was specifically designed to exploit the one-way nature of most multimedia communication in which large amounts of information flow toward the user and only a small amount of interactive control information is returned.

How does ADSL work?

ADSL modems convert the copper twisted-pair telephone lines into a high-speed digital pipe. That means you could be simultaneously talking on the phone or sending a fax - while surfing the World Wide Web.

What are the Benefits of ADSL?

• Simultaneous Internet and voice/fax capabilities over a single telephone line
• Uninterrupted, high-speed Internet access that's always on-line
• Cost-effective solution for residential customers, telecommuters and small businesses
• Data Security that exceeds other technologies
• Fast download speeds especially multimedia content.

What are the Disadvantages of ADSL?

The technology is distance-sensitive:
If you're more than a couple of miles from the phone company central office, ADSL can be slower or unavailable.

ADSL VS ISDN

The two services are not the same --

• ISDN provides two voice channels or a 128Kbps data channel while ADSL is predominantly a data pipe providing an asymmetrical bandwidth .
• The power for ADSL is sent by the carrier over the copper wire; as with conventional phone service, the line works even when local power fails. That's an advantage over ISDN, which requires a local power supply.