3. ADSL Overview

3.1 What is ADSL?

Asymmetric Digital Subscriber Line (ADSL) is:

• A Telephone Loop Technology that uses existing phone lines
• Provides high-speed data and analog voice (Data over Voice)
• Dedicated digital line for an IP connection
• Data rates (North America) combinations of :
  Upstream/downstream
  256 kbps/256 kbps
  384 kbps/128 kbps
  384 kbps/384 kbps
  384 kbps/1.5 Mbps
  and many others
  
• Wide range of CPE options, including Ethernet 10baseT Interfaces.
• Dedicated ISP connection (static or dynamic addresses)
• Can support an IP subnet (from 1 to 254 IP addresses, depending on ISP)
• Priced lower than dedicated private line (T1) connections

3.2 ADSL Applications

ADSL was designed to provide a dedicated, high-speed data connection for Internet/Intranet Access, using existing copper phone lines. This allows ADSL to work on over 60-80% of the phone lines existing in the U.S. without modification. Additionally, ADSL provides speeds approaching T1 (1.5Mbps), which are much greater than analog modems (56kbps) or ISDN (128kbps) services provided over the same type of line. ADSL is usually priced to be much less other dedicated digital services, and is expected to priced somewhere between T1 and ISDN services (including the ISDN usage charges).

The Telcos see ADSL as a competitive offering to the Cable Company's Cable Modems, and as such, are expected to provide competitive pricing/configuration offerings. Although Cable Modems are advertised as having 10-30Mbps bandwidth, they use a shared transmission medium with many other users on the same line, and therefore performance varies, perhaps greatly, with the amount of traffic and other users.

ADSL is positioned for Home and Small Office (SOHO) applications that require high-speed Internet Access. Since it also provides dedicated access, It can be used for interconnecting low-bandwidth servers to the Internet, and would provide a great access solution for 5-20 PCs in an Office location. It is also a great solution for those Linux power users that just want high speed access from home:-).

3.3 What is xDSL/DSL?

Digital Subscriber Line (DSL) provides a dedicated digital circuit from your home to the Telcos central office, using analog telephone line. DSL also provides a separate channel for voice phone conversations, which means analog calls (voice, fax. etc.) can be carried at the same time high-speed data is flowing across the line. DSL uses the frequency spectrum between 0kHz-4kHz for Analog Voice, and 4kHz-2.2MHz for data. xDSL is a generic acronym for a family of dedicated services, where the " x"stands for:

• ADSL Asymmetric Digital Subscriber Line: 1.5 Mbps-384kbps/384-128kbps
• HDSL High-bit-rate Digital Subscriber Line: 1.5 Mbps/1.5 Mbps (4Wire)
• SDSL Single-line Digital Subscriber Line: 1.5 Mbps/1.5 Mbps (2Wire)
• VDSL Very high Digital Subscriber Line: 13 Mbps-52 Mbps/1.5 Mbps- 2.3 Mbps.
• IDSL ISDN Digital Subscriber Line: 128 Kbps/128 Kbps.
• RADSL Rate Adaptive Digital Subscriber Line: 384kbps/128kbps
• UDSL Universal Digital Subscriber Line: 1.0Mbps-384kbps/384kbps-128kbps
  also called " splitterless" DSL or DSL-Lite, as it doesn't require a splitter.

where Xbps/Ybps is X=Downstream Bit rate, Y=Upstream Bit rate

3.4 Why so many speeds?

ADSL has to work over existing phone lines, which were designed 100 years ago, and were never designed for digital services (See the FAQ answers for more information). Also, ADSL is a new service, and all the providers are trying to find the right price/feature combinations that will make it in the market.

For the average user, the basic way of thinking about it is to segment the options into three categories:

• Low End Residential

    Speed ranges from 384kbps-128kbps, Asymmetric

• High End Residential or Business End User

    Speed ranges from 1.5Mbps-384kbps, Asymmetric

• High End Server

    Speed ranges from +2.0Mbps-1.1kbps, Symmetric