Summary

48 IT Essentials: PC Harware and Software Companion GuideFigure 8-25ModemsAn internal modem plugs into an expansion slot on the motherboard. To configure amodem, jumpers may have to be set to select the IRQ and I/O addresses. No configurationis needed for a “plug-and-play” modem, which can only be installed on a motherboard thatsupports 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 themodem to work properly. Drivers for modems are installed the same way drivers areinstalled 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. Thismeans that modems can duplicate the dialing characteristics of a telephone. DUN creates aPoint-to-Point Protocol (PPP) connection between two computers over a phone line.After the line connection has been established, a “handshaking sequence” takes placebetween the two modems and the computers. The handshaking sequence is a series of shortcommunications that occur between the two systems. This is done to establish the readinessof the two modems and computers to engage in data exchange. Dialup modems send dataover the serial telephone line in the form of an analog signal. Because the analog signalschange gradually and continuously, they can be drawn as waves. In this system, the digitalsignals are represented by 1s and 0s. The digital signals must be converted to a waveform totravel across telephone lines. The receiving modem converts them back to digital form, 1sand 0s, so that the receiving computer can process the data.