Analog Modems

In this article we will discuss Analog Modems, will make brief discussion on Analog Modems, last article we discuss about DCAP.

A modem used for asynchronous transmission of data over Plain Old Telephone Service (POTS) lines. Analog modems are still a popular component for remote communication between users and remote networks.

The word «modem» stands for “modulator/demodulator,” which refers to the fact that modems convert digital transmission signals to analog signals and vice versa. For example, in transmission, an analog modem converts the digital signals it receives from the local computer into audible analog signals that can be carried as electrical impulses over POTS to a destination computer or network.

To transmit data over a telephone channel, the modem modulates the incoming digital signal to a frequency within the carrying range of analog phone lines (between 300 Hz and 3.3 kHz). To accomplish this, multiplexing of the digital signal from the computer with a carrier signal is performed. The resulting modulated signal is transmitted into the local loop and transmitted to the remote station where a similar modem demodulates it into a digital signal suitable for the remote computer.

Bell Labs in the 1960s and 1970s originally formulated modem standards, but after the breakup of Bell Telephone, the task of developing modem standards was taken over by the International Telegraph and Telephone Consultative Committee (CCITT), which is now called the International Telecommunication Union (ITU). According to ITU specifications, modem standards are classified by a series of specifications known as the V series.

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