Broadband

Digital Subscriber Line technology, commonly known as DSL, uses a standard two-wire copper pair (or line) that exists in almost every home and office to transmit data at 2 Mbps or faster.  The speed depends on your location, line quality (fiber or copper) and the distance to the local phone company's Central Office – the main switching station for phone lines in a designated geographical area.

DSL hardware splits the phone line into two frequency ranges.  Frequencies below 4 kHz are used for voice.  The range above is used for data.  DSL transmits data and images over existing copper wires at a much faster speed than dial-up analog modems. Because DSL is always connected, there are no dial-up delays.

DSL’s always-on connection is not subject to usage-sensitive pricing, which means the service can be used any time for as long as you need without incurring usage charges.

Typically, high-speed DSL services are available to customers who live or work within a three-mile radius of the nearest Central Office.  About 50 to 60 percent of all U.S. homes are currently DSL compatible.  The various types of DSL, including ADSL, SDSL and IDSL, have different performance characteristics and pricing.

ADSL

Operating over a normal telephone line, an Asymmetric Digital Subscriber Line (ADSL) can be used to send and receive high-speed digital data and make normal voice calls at the same time. 

Unlike high-speed cable Internet services, an ADSL circuit doesn’t compete for bandwidth with other users.  Besides being extremely fast – 40 to 50 times faster than a dial-up connection – ADSL may be cheaper in the long run if you spend a lot of time on the Internet via a dial-up connection.

The ADSL signal is carried by two DSL modems, one at the user end and one at the local phone exchange.  The modems are designed to exploit the physical transmission capabilities of existing copper telephone lines, resulting in high data-transfer rates.

Speed is ADSL’s biggest advantage.  A standard modem can reach speeds of up to 56 Kbps, while an ISDN line reaches speeds of up to 128 Kbps.  ADSL, on the other hand, can attain speeds of up to 6.1 Mbps, accelerating the download of graphics, multimedia and large data files.

What’s more, the ADSL connection is always “on.”  There are no dropped connections, and you won’t waste valuable time trying to establish a dial-up connection with your service provider.

Using ADSL, up to 6.1 megabytes per second of data can be sent downstream and up to 640 Kbps upstream.  The high downstream bandwidth means that your telephone line will be able to bring motion video, audio, and 3-D images to your computer or hooked-in TV set. In addition, a small portion of the downstream bandwidth can be devoted to voice rather than data, and you can hold phone conversations without requiring a separate line.

This asymmetry, combined with always-on access (which eliminates call setup), makes ADSL ideal for Internet/intranet surfing, video-on-demand, and remote local area network (LAN) access. Users of these applications typically download much more information than they send.

SDSL

Using conventional copper circuits, Symmetric Digital Subscriber Line (SDSL) services provide fast, reliable connections to the Internet, and between multiple branch offices.  Unlike ADSL, SDSL lines deliver images and data at the same upload and download speeds.

Like ASDL, SDSL is a dedicated service, meaning it is always connected.  No more busy signals, and no more waiting for your modem to connect to the Internet.  A single click of the mouse and you're on-line.

SDSL offers high-speed Internet access at a fraction of the cost of other dedicated services, such as a T1 line. T1 lines can cost more than $1,000 per month, while SDSL is priced up to 70 percent less, offering small and midsize businesses affordable high-speed access.

SDSL is a great alternative for businesses that host a Web server and sell products or services online, conduct video conferencing or video streaming, send or receive e-mail with large attachments, or want to begin using the Internet as a business tool.

IDSL

An ISDN Digital Subscriber Line (IDSL) delivers data at up to 144 Kbps in each direction and can be provisioned on any ISDN-capable phone line.  Unlike ADSL and other DSL technologies, IDSL signals can travel over copper lines equipped with electronics (e.g., amplifiers and repeaters) and can be deployed regardless of the distance the user is from the Central Office.   

IDSL is symmetrical, similar to SDSL, but operates at slower speeds and longer distances.  Unlike ISDN, IDSL is always connected, operating at symmetric 144 Kbps speeds without usage charges.

IDSL circuits typically carry only data (not voice) and offer transfer rates that are about the same as ISDN (144 Kbps vs. 128 Kbps).  One of the major benefits of IDSL is its always-on connection, which eliminates call-setup delays.  Customers also benefit from flat-rate billing, instead of per-minute fees.

If you live or work far from the nearest Central Office, outside the ADSL and SDSL coverage area, an IDSL connection may be your only viable DSL option.