Differences between ADSL and dial-up, ISDN modems

[Gauresh]

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

[Aadarsh]

ISDN runs at 64kbps or 128kbps :

ADSL can potentially download at 8Mbps Many home ADSL services are provided at around 512kbps.

PSTN stops you using your phone. ADSL allows you to surf and phone at the same time.

[ADITYA_M]

• ADSL modem is permanently connected, it may be necessary to take action on your PC to make the connection to the Internet.
• Services like fax and voice can be provided over the ADSL data
• connection to the Internet.
• In practice, a typical download speed on a home ADSL service will be
• up to 400kbps