Telephone modem

A modem is a communications device for transferring digital information (from a computer) to another digital device using Analogic lines, typically network Telephone. Communication is usually a connection Internet but can also be a transfer between two remote computers. To transfer data, the modem uses the modulation frequency: the signal is modulated on a fixed carrier frequency in the range audible. The signal frequency varies then obtained based on the data transmitted.

The term is mainly used in network switched telephone and ISDN, more rarely, except with ADSL external equipment using the USB port, as opposed to routers.

A modem can be internal, generally connected in a PCI bus (older ISA) or specialized bus as the AMR or CNR. These are used by Win Modems. In the case of a ISA bus, device is automatically associated with a port number so hardware (Com 1 to 4). Emulate a PCI versions serial port (Driver specific operating system) and a specific driver electronic circuit. In the case of external versions, they along the lines connecting via an USB port, serial port for older models.

Different standards define the RTC transmission rates and error correction. The current equipment on telephone lines are standard V90 or V92. For both versions, the baud rate in reception expressed in baud (Maximum of 56 Kb / s) exceeds the issue (limited to 33.600 and 48.000 bps). The V92 allows more cut the connection and then resume when call. This solution must still be implanted in the ISP (Internet Servive Provider).

Associated definitions: ADSL - ISDN