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(also modulator-demodulator)

Modem definition

A modem is a device that allows computers to transmit data over analog transmission mediums like telephone lines or cable networks. Modems can encode digital data into analog signals and decode it back again at the receiving end of the connection.

Modems are often confused for routers, but they serve different (albeit complimentary) roles. A router connects devices together to form a network. This router is connected to a modem, which connects the network to an internet service provider (ISP) and the broader internet. In practice, router and modem functions are frequently integrated into a single device known as a “gateway.”

See also: DSLAM, area border router, customer edge router, default gateway

Examples of modems

  • Dial-up: Dial-up modems use standard telephone lines for data transmission, with a maximum connection speed of 56 Kbps. Dial-up modems are the oldest and slowest modem type, now mostly replaced by fast broadband connections.
  • Cable: Cable modems are a subtype of broadband (technology capable of providing more speed than telephone lines or other voice grade channels) modems. Cable modems connect to cable television networks.
  • DSL: Digital subscriber line (DSL) modems are another subtype of broadband modems. DSL modems provide high-speed internet access over telephone lines, but their signals are not transmitted through ordinary phone exchanges — instead, DSL signals are received by digital subscriber line access multiplexers (DSLAMs) at the phone company’s central office.
  • Wireless (mobile): Wireless modems provide internet access over cellular networks. Wireless modems are typically installed directly into mobile devices like smartphones, tablets, and laptops, although they may also be attached to the device as a peripheral (such as a USB dongle).