Networking Guide : Network Components


Modem means modulator-demodulator. At the sending end, a modem modulates a carrier with the data (baseband signal) to prepare it for transmission. At the receiving end, the modulated carrier is demodulated (i.e. converted back to the original shape) and the data is extracted. There are many types of modulation techniques used in modem design, e.g. PCM, QPSK, QAM. A modem also performs other functions, such as digital-to-analog/analog-to-digital conversion, compression/decompression, error correction, and encryption/decryption.

Picture: Modem in Internet access
A modem at a subscriber site communicates with the corresponding modem at her Operator or ISP.

You must connect your computer to a modem or install an internal modem inside your computer when you want to connect to the Internet. The type of modem that you need depends on the Internet access method that you choose. You may need a voiceband modem, a cable modem, an ADSL modem, or a GPRS modem. Your modem will communicate with the corresponding modem at your ISP during an Internet connection, transmit your computer message to the ISP (upstream), and receive Internet content forwarded by the ISP (downstream).

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