Describe the Installation of a Modem

A modem, shown in Figure 8-25, is an electronic device that transfers data between one computer and another using analog signals over a telephone line. The modem converts digital data to analog signals for transmission. The modem at the receiving end reconverts the analog signals to digital data to be interpreted by the computer. The process of converting analog signals to digital and back again is called modulation/demodulation. Modem-based transmission is very accurate, despite the fact that telephone lines can be noisy because of clicks, static, and other problems.

Figure 8-25 Modems

An internal modem plugs into an expansion slot on the motherboard. To configure a modem, jumpers may have to be set to select the IRQ and I/O addresses. No configuration is needed for a "plug-and-play" modem, which can only be installed on a motherboard that supports plug and play. A modem using a serial port that is not yet in use must be configured. Additionally, the software drivers that come with the modem must be installed for the modem to work properly. Drivers for modems are installed the same way drivers are installed for NICs.

External modems connect to a computer through the serial and USB ports.

When computers use the public telephone system to communicate, this is called dialup networking (DUN). Modems communicate with each other using audio tone signals. This means that modems can duplicate the dialing characteristics of a telephone. DUN creates a Point-to-Point Protocol (PPP) connection between two computers over a phone line.

After the line connection has been established, a "handshaking sequence" takes place between the two modems and the computers. The handshaking sequence is a series of short communications that occur between the two systems. This is done to establish the readiness of the two modems and computers to engage in data exchange. Dialup modems send data over the serial telephone line in the form of an analog signal. Because the analog signals change gradually and continuously, they can be drawn as waves. In this system, the digital signals are represented by 1s and 0s. The digital signals must be converted to a waveform to travel across telephone lines. The receiving modem converts them back to digital form, 1s and 0s, so that the receiving computer can process the data.

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