DSL And ADSL- Is There Any Difference?
DSL and ADSL are really just general and specific terms, respectively, for the type of high speed internet service widely available on phone lines today. DSL stands for Digital Subscriber Line and ADSL is Asymmetric Digital Subscriber Line. The word 'digital' refers to the ability of the line to transport signals in the form used by the computer, which is 'binary' or a series of ones and zeroes. Traditionally, telephone transmissions were analog (consisting of electronic pulses), which meant that any computer connections through regular phone lines would require modems. The word modem comes from 'modulator/demodulator' which comes from the neccesity of modulating (changing the data to analog for transmission) and demodulating (changing back to digital for use at the computer). DSL and ADSL connections do not require modems.
So what is the difference between DSL and ADSL? Actually, ADSL is just one of a number of different types of DSL. The 'asymmetric' in ADSL refers to the fact that upstream and downstream speeds are not symmetrical. The speed of the transmission from the Internet to the computer (downstream) will normally be faster than the speed of the connection from the computer to the Internet (upstream).
ADSL is the most common form of DSL in use, because it fits the Web access needs of most users. Most people download a lot more information from the Internet than they upload to it. The slowest version of ADSL available in most locations nowadays is 256 Kbps downstream and 128 Kbps upstream. Usually, faster versions will increase the downstream transfer rate much more quickly than the upstream. The downstream speed does typically not increase past 128 Kbps until the upstream rate is higher than 768 Kbps. There actually are technicalities inherent in the DSL connection that make it easier for the provider to supply a service that is faster upstream than downstream. Since this fits perfectly with most residential customer's use, ADSL became the de facto solution for home use. However, those who upload larger quantities of data ( business or professional customers such as website creators or designers, for example) can utilize a form of DSL called SDSL, or Symmetric Digital Subscriber Line, which offers identical transmission speeds in both the upstream and downstream direction.
There are still more versions of DSL available. Technically, the umbrella term to indicate that one is talking about all versions of DSL in general is xDSL, but most people just refer to it as DSL. Some other types are HDSL for High data rate Digital Subscriber Line, IDSL for IDSN Digital Subscriber Line, VDSL for Very high data rate Digital Subscriber Line, and DSL-Lite, which does not require a splitter at the place of installation. It's probably not important to know anything about these various options. If you have access to DSL at your home, it will most likely be ADSL, with the occasional option of SDSL.
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