Deﬁnition: Dial-up connections are network connections that use telecommunications media, such as modems, phone lines, and long-distance carrier services, to provide low-cost, low-bandwidth WAN connectivity and remote network access. The use of dial-up as a primary connection method is becoming rare, and because they are generally limited to 56 Kbps, these connections are mostly used as backups for higher-bandwidth WAN services.
Figure: Dial-up connections
The ordinary home and business phone lines used for dial-up connections are part of the Public Switched Telephone Network (PSTN). Sometimes you will see the PSTN referred to casually as POTS, for Plain Old Telephone Service.