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Chapter 28. Voice Over Internet Protocol

Chapter 28. Voice Over Internet Protocol

Voice over Internet Protocol (VoIP) is a technology to use the Internet Protocol instead of phone-switching technology for voice, facsimile, and message services. The typical consumer probably hasn't heard of VoIP yet. However, the technology is already commonly in use. The main example would be the dominance of inexpensive prepaid telephone cards on the market. VoIP is the technology in use for almost all the prepaid telephone long-distance cards. It's how their per-minute charges are so competitive, compared with traditional long-distance service.

Until just a few years ago, every telephone call utilized the traditional Public Switched Telephone Network (PSTN). With PSTN, a long-distance call first goes through a local telephone company, then to the long-distance provider (for a connection fee) in an all-analog voice signal. Large telephone switches are in place to make the transfer. With VoIP prepaid telephone cards, you pick up your phone and dial a special number, then the long-distance number. The route that the call takes differs from that of traditional PSTN. VoIP simplifies the system with an advanced combination of hardware and software. The analog call is converted to digital. The digitized call is compressed and translated into IP packets for transmission over a private IP network or the Internet. The call bypasses the traditional route through the expensive telephone switch at a telephone company's central office. At the other end of the wire, the process is reversed: The digital signal is converted back to an analog signal, and it's again routed through regular telephone equipment.


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