"x" Digital Subscriber Line

(X-D-S-L)

Any of the DSL telephone technologies (a small "x" is often used to represent "anything").

When two modems connect via a telephone circuit the modems effectively use the voice bandwidth for their communication (digital signals are converted to analog and then back to digital at the other end). Most phone companies , however, will take the analog from the phone and convert it to digital for transmission through the phone network. It is only converted back to analog just before the receiving line. So, using a modem in this fashion is inefficient as phone lines can handle significantly more bandwidth. If the sending and receiving phones could send and receive digital data directly then the bandwidth a phone line could carry could increase greatly (depending on distance to the phone company office).

This is basically what xDSL does. It sends digital data directly into the phone lines at a higher data rate; still allowing the analog data for voice to also be sent over the same lines.

There are a variety of flavors, summarized below

Summary of xDSL Services

• ADSL: Asymmetric service with 8Mbps downstream and 640Kbps upstream with phone service using a single copper pair.
• G.lite: Asymmetric service with 1.5Mbps downstream and 640Kbps upstream with phone service using a single copper pair.
• ASL Lite: Asymmetric service with 384Kbps downstream and 384Kbps upstream with no phone service using two copper pairs.
• HDSL: Symmetric service with 1.5Mbps downstream and 1.54Mbps upstream with no phone service using two copper pairs.
• HDSL2: Symmetric service with 1.54Mbps downstream and 1.54Mbps upstream with no phone service using a single copper pair.
• IDSL: Symmetric service with 144Kbps downstream and 144Kbps upstream with no phone service using a single copper pair.
• SDSL: Symmetric service with 2.3Mbps downstream and 2.3Mbps upstream with no phone service using a single copper pair.
• VDSL: Symmetric or asymmetric service with 51Mbps downstream and 51Mbps upstream with phone service using a single copper pair.

More Information

• DSL Technology Article