Network Modems

Network modems (modulators-demodulators) are devices or programs that allow computers to transmit data over telephone lines. They convert digital computer data to analog sound waves and then demodulate the carrier signals to decode the transmitted information. There are two form factors for network modems: internal and external. Internal modems are computer cards that attach to a computer through a slot. External modems are modules or devices that connect to a larger system through a physical port. In terms of connectivity, several device types are commonly available. Public switched telephone network (PSTN) modems transmit analog data across copper telephone wires. Integrated services digital network (ISDN) devices can transmit data over regular telephone lines or digital telephone lines. Network modems that use digital subscriber lines (DSL) support standard xDSL or variants such as asynchronous DSL (ASDL), symmetric DSL (SDSL), or high data rate DSL (HDSL). Cable modems operate over cable television lines and can achieve very high data rates. Fiber optic modems are also available.

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