Any telecommunications link that is serviced by a modem. Dial-up lines are ordinary phone lines used for voice communication, while dedicated or leased lines are digital lines with dedicated circuits.
Dial-up lines are generally much less expensive to use, but they have less available bandwidth.
Companies often use dial-up lines for occasional, low-bandwidth usage (such as remote access networking) or as a backup for more costly dedicated lines. Dial-up lines are shared with all subscribers in the Public Switched Telephone Network (PSTN) domain, while dedicated or leased lines are allocated solely to the subscriber’s private telecommunications domain.