History of Computers - DSL

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DSL[1] is a high-speed Internet service like cable Internet. DSL provides high-speed networking over ordinary phone lines[2] using broadband modem technology. DSL technology allows Internet and telephone service to work over the same phone line without requiring customers to disconnect either their voice or Internet connections.[3] DSL is an internet system used mainly in homes and small businesses. DSL is also called xDSL and is used to refer to the different #Types of DSL. DSL performance increases with proximity to ISP's offering DSL services. If this is the case, a user may be able to receive data at effective rates up to 6.1MB/s (the theoretical limit of DSL is 8.44MB/s), enabling streaming motion video, audio, and even 3-D effects.[4]

Overview

How it Works

A traditional phone service is able to connect one's home or small business to a telephone company office through copper wires called "twisted pairs"(Copper wires that are wound around each other) The traditional phone service was initially created to allow a person to exchange voice information wither other phone users, using an analog signal. A phone works by converting acoustic signals and converting them into an electrical equivalent in terms of volume[5] and pitch[6] Since a telephone company's signaling is already set up for this type of analog wave transmission, it is easier to exchange information with the telephone company. This is why a computer needs a modem, so it is able to demodulate[7] the analog signal.

The copper wires used to connect a phone line have a lot of room and can support more than telephone conversations -- they are capable of handling a much greater bandwidth[8] than that demanded for the voice. DSL takes advantage of this "extra capacity" in order to carry information through the wire without disturbing a telephone conversation. This entire process is based off of matching particular frequencies to particular tasks. Digital Subscriber Line is a technology that assumes digital data does not require change into analog form and back. Digital data is transmitted to your computer directly as digital data and therefore is able to take advantage of the leftover space on the copper wire.

Types of DSL

ADSL

The variation called ADSL[9] is the form of DSL that will become most familiar to most users. Many homes and small business users are connected to an ADSL line. ADSL divides up the available frequencies in a line on the assumption that most Internet users look at, or download, much more information than they send, or upload. Under this assumption, if the connection speed from the Internet to the user is three to four times faster than the connection from the user back to the Internet, then the user will see the most benefit most of the time. See more about ADSL

CDSL

CDSL[10] is a variation of DSL, trademarked by Rockwell International Corporation that is somewhat slower than ADSL. CDSL has the advantage of not requiring a 'splitter' on the user's end of the DSL. However, Rockwell no longer provides information about CSDL at its Web site and does not appear to be marketing it.

DSL Lite

DSL Lite[11]is a slower version of DSL that doesn't require splitting at the user's end, but rather remotely manages to split the DSL signal at the telephone company end. DSL Lite is expected to become the most widely installed type of DSL in the future.

HDSL

HDSL[12] is one of the earliest forms of DSL. HDSL is used for wideband digital transmission within a corporate site and between the telephone company and a customer. The main characteristic of HDSL is that it is symmetrical: an equal amount of bandwidth is available in both directions.

RADSL

RADSL[13] is an ADSL technology from Westell in which software is able to determine the rate at which signals can be transmitted on a given customer phone line and adjust the delivery rate accordingly.

VDSL

VDSL[14] is a developing technology that promises much higher data rates over relatively short distances (between 51 and 55 Mbps over lines up to 1,000 feet or 300 meters in length). It's envisioned that VDSL may emerge somewhat after ADSL is widely deployed and co-exist with it. The transmission technology (CAP, DMT, or other) and its effectiveness in some environments is not yet determined. A number of standards organizations are working on it.


Significance

DSL is significant to computer history because it helped to revolutionize the way we are able to connect to the internet. Before DSL, an internet connection would interrupt telephone lines making it virtually impossible to make a phone call and be on the internet at the same time. With the application of DSL, people were permitted to make telephone calls to and from areas where internet was in use.


Links

References

  1. ↑ Digital Subscriber Line
  2. ↑ Specifically, copper telephone lines that exist in today's phones.
  3. ↑ Definition found at About DSL
  4. ↑ Information found at Fast Guide to DSL
  5. ↑ Signal amplitude
  6. ↑ Frequency of wave change
  7. ↑ Converting analog signals back into digital signals
  8. ↑ Range of frequencies
  9. ↑ Asymmetric Digital Subscriber Line
  10. ↑ Consumer DSL
  11. ↑ AKA G.Lite, splitterless ADSL, and Universal ADSL
  12. ↑ High bit-rate Digital Subscriber Line
  13. ↑ Rate-Adaptive DSL
  14. ↑ Very High Rate DSL
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