Dial-up Internet access

Dial-up Internet access is a form of Internet access that uses the facilities of the public switched telephone network (PSTN) to establish a connection to an Internet service provider (ISP) by dialing a telephone number on a conventional telephone line which could be connected using an RJ-11 connector. Dial-up connections use modems to decode audio signals into data to send to a router or computer, and to encode signals from the latter two devices to send to another modem at the ISP.

Dial-up Internet reached its peak popularity during the dot-com bubble. This was in large part because broadband Internet did not become widely used until well into the 2000s. Since then, most dial-up access has been replaced by broadband.

In 1979, Tom Truscott and Jim Ellis, graduates of Duke University, created an early predecessor to dial-up Internet access called the Usenet. The Usenet was a UNIX-based system that used a dial-up connection to transfer data through telephone modems.

Dial-up Internet access has existed since the 1980s via public providers such as NSFNET-linked universities in the United States. In the United Kingdom, JANET linked academic users, including a connection to the ARPANET via University College London, while Brunel University and the University of Kent offered dial-up UUCP to non-academic users in the late 1980s.

Commercial dial-up Internet access was first offered in 1989 in the US by the software development company Software Tool & Die, with their service called "The World". Sprint and AT&T in 1992 also began offering internet access, along with Pipex in the United Kingdom. After the introduction of commercial broadband in the late 1990s, dial-up became less popular. In the United States, the availability of dial-up Internet access dropped from 40% of Americans in the early 2000s to 3% in the early 2010s. It is still used where other forms are not available or where the cost is too high, as in some rural or remote areas.

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, 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.

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".