1. What is DSL?
  2. How is DSL different from analog modems?
  3. What are common DSL applications?
  4. What are the advantages of DSL over cable modems?

What is DSL?

Digital Subscriber Line (DSL) refers to a set of modem-like technologies that provide high bandwidth over existing copper cable. The same type of cable used for your telephone wire. It exists over the connection between two points without amplifiers or repeaters along the cable route. DSL requires a terminating device at each end of the cable that supports the data stream, usually in a digital format, and overlays it onto a high speed analog signal. Various modulating techniques are used to support DSL and include 2B1Q, CAP, and DMT.

Types of DSL currently in use include SDSL, HDSL, ADSL, IDSL and VDSL.


How is DSL different from analog modems?

DSL technologies use a wider band of frequencies, thus achieving data transmission rates that are up to 300 times faster than analog modems. Furthermore, unlike analog modems, DSL transmissions do not pass through the regular voice telephone network. They are directly connected to the data network. This element of DSL can clear the "congestion" in the voice telephone network that a lot of dial-up Internet traffic causes.


What are common DSL applications?

  • High speed Internet access
  • Corporate intranets
  • Local telephone exchange operations
  • Campus environments
  • Multiple Dwelling or Tenant Units (MDU/MTU)

What are the advantages of DSL over cable modems?

Copper lines are abundant and provide efficient service, all around the world. This fact alone gives DSL a clear advantage over cable modems. While copper phone lines are already prevalent in homes and businesses everywhere, coaxial cable is not (especially at business locations around the world).

Cable modem companies are quick to point out the speeds at which their products transmit data upstream or downstream. However, those speeds decrease significantly when multiple users in a neighborhood serviced by cable modems log on at the same time. Cable modem companies cannot guarantee their users a specific amount of bandwidth. Because DSL is an individual subscriber service, a specific amount of bandwidth is guaranteed.

DSL has many other significant advantages, including:

Security -Cable modems operate on a shared line. Therefore, security is a much greater issue for cable modem users. although encryption improves cable modem security, it also increases overhead. DSL is a dedicated, individual subscriber service, thus providing far better user security. ¡P

Speed -DSL enables full use of phone line's bandwidth. Conversely, cable modem users are able to use just a fraction of a cable modem's potential speed, and as more cable modem users go online, their throughput will be even lower.

Reliability -Cable networks are known for more frequent periods of downtime. As previously mentioned, DSL is very reliable because it operates over the same copper wiring used for phone lines.

Interactive -DSL offers interactive capability. Cable modems are generally usable only for broadcasting to the subscriber.