ADSL exploits the unused analogue bandwidth that is potentially available in the wires that run from the user premises to the local exchange. This wiring was designed to carry that portion of the frequency spectrum that is occupied by normal speech. The wires can, however, carry frequencies above this rather limited spectrum. This is the portion that ADSL uses.
So, what are the inherent differences between ADSL and 'traditional' dial-up modems and ISDN?
- PSTN and ISDN are dial-up technologies
- ADSL is 'always-on'
- ADSL is un-metered and charged at a flat-rate
- PSTN and ISDN allow you to use fax, data, voice, data to the Internet, data to other devices
- ADSL is just about data to the Internet
- PSTN and ISDN allow you to choose the Internet Service Provider you want to use
- ADSL connects you to a pre-defined ISP
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