DSL describes a family of technologies that try to offer a high-capacity data rate over a standard copper telephone line.
When I was talking about modem standards, I mentioned that that the passband of the local loop is only about 3000Hz. This is generally caused by limitations of the equipment at the exchange, rather than any limitation of the copper wire itself. If this equipment is replaced, then data can be sent across a wider range of frequencies than those available to the standard telephone system (300Hz – 3400Hz). Although the signal will be more distorted when using frequencies higher than 3400Hz to transmit data, sophisticated equipment at the subscriber's end which acts an equaliser can compensate for this. This equipment is known as a DSL modem.

Click here for more details on specific types of DSL, namely ADSL, SDSL and VDSL.


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Introduction - Modems - ISDN - DSL - cable modems - Mobile comms - Conclusion - Glossary