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Telecommunications Software
Published in Paul W. Ross, The Handbook of Software for Engineers and Scientists, 2018
Procomm Plus or any terminal program needs several items to communicate with other computers: A modem—A modem is a computing device that allows your computer to send a digital signal over analog phone lines to a remote computer. The remote computer also uses a modem to translate the signal you sent into understandable commands. The modem should also be Hayes compatible (most PC modems are). It does not matter if the modem is internal or external to your computer.A telephone line—The modem needs to be connected to a telephone line. The line need not be used only by the modem. It could be the phone line into your home or apartment. Just be sure when you are using the modem no one picks up or attempts to use any of the other extensions. At best, you will see garbage on your screen or your modem will hang up the phone.An available serial port—Most personal computers have several serial communications ports available. Often one is used for the mouse; the other should be available for your modem.
Cable Modems
Published in Keshab K. Parhi, Takao Nishitani, Digital Signal Processing for Multimedia Systems, 2018
A cable modem is a device that sits on a coaxial cable network and transmits to, and receives from, the network modulated digital data. By coaxial cable network we mean a network that was originally designed for broadcast of analog television signals. In what follows, for clarity we discuss US cable systems only. The user should understand that there are several differences between US and, for example, European cable but the philosophy of cable modem design and most of the problems encountered are essentially the same. As the emphasis of this book is on digital signal processing we also concentrate on the physical layer of the system where the modulation and demodulation occurs.
Communications Technologies
Published in Sharon Yull, BTEC National for IT Practitioners: Core Units, 2009
Analogue transmission is used to carry voice, data or fax, and has a limited bandwidth. Using a waveform, messages are carried by a cable such as a telephone line. Analogue information is transmitted by modulating a continuous transmission signal. A modem, for example, modulates data that is received over a telephone line in analogue to a digital format that can be understood by a computer and demodulates received signals to retrieve data.
Telephone networks, BBSes, and the emergence of the transnational ‘warez scene’
Published in History and Technology, 2019
The era of such convergence organized by computer users began a year after the publication of the aforementioned Science paper. But its basic concept came not from the circle of ARPANET engineers, but rather from a thriving American computer hobbyist community. In 1978 a computer hobbyist, Ward Christensen designed a convenient system of connecting personal computers by telephone lines with a modem (from ‘modulation/demodulation’). Previously modems were used in institutional and commercial settings. Only in the late 1970s did modem manufacturer Hayes Microcomputer Products begin offering its modems in retail trade for the growing community of computer hobbyists. Christiansen noted that he had used a Hayes modem while designing a BBS system.15 The modem provided an interface between computers and analog telephone lines by changing (modulating) 1 and 0 into two different predefined sound frequencies transmitted over the phone. Both frequencies were later transferred back (demodulated) to 1 and 0 by a receiving modem. This system was called a Bulletin Board System, and, as the name suggests, it was supposed to provide geographically dispersed computer hobbyists with their version of conventional bulletin boards, one of the material centers of social life in local communities. What was required for establishing a BBS node, usually referred to as a ‘board’, or calling other BBSes, was simply a computer with dedicated software mostly distributed as freeware, a modem, and an access to a telephone line. Using telephone lines for sending data rather than for voice calls came to be accepted by the telecoms under the condition that a modem be certified with the FCC (or a similar agency in another country) to prove that the technology did not cause any interference for the telephone network.