Editing Dial-up Internet access (section)

== Modems ==
{{main|Dial-up modem}}
[[File:Modem-bank-1.jpg|thumb|Banks of modems used by an ISP to provide dial-up Internet service]]
Because there was no technology to allow different carrier signals on a telephone line at the time, dial-up Internet access relied on using audio communication. A modem would take the digital data from a computer, [[modulation|modulate]] it into an audio signal and send it to a receiving modem. This receiving modem would [[demodulate]] the signal from modulating analogue noise and demodulating it back into digital data for the computer to process via a modem that would decode the data, and send it to the computer.<ref name=":0">{{Cite web|last=Quine|first=Alison|date=2008-01-28|title=Modem (Modulation/Demodulation) Definition|url=https://www.itprc.com/modem-modulationdemodulation-definition/|access-date=2021-06-14|website=ITPRC|language=en-US}}</ref>

The simplicity of this arrangement meant that people would be unable to use their phone line for verbal communication until the Internet call was finished.

The Internet speed using this technology can drop to 21.6 [[kbit/s]] or less. Poor condition of the telephone line, high noise level and other factors all affect dial-up speed. For this reason, it is popularly called the 21600 Syndrome.<ref>{{cite web |url=http://www.usrmodem.ru/documents/articles/symbrate.shtml |title=СИHДРОМ 21600/V34 или Правда о том, как USR выбирает Symbol Rate |website=www.usrmodem.ru |access-date=11 January 2022 |archive-url=https://web.archive.org/web/20210715084533/http://www.usrmodem.ru/documents/articles/symbrate.shtml |archive-date=15 July 2021 |url-status=dead}}</ref><ref>{{Cite web|url=https://forum.ixbt.com/topic.cgi?id=32:796|title=Синдром 21600 как с ним бороться ? [1] - Конференция iXBT.com|website=forum.ixbt.com}}</ref>