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VoIP and Unified Communications: Internet Telephony and the Future Voice Network by William A. Flanagan

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1

IP TECHNOLOGY DISRUPTS VOICE TELEPHONY

Packet voice, Voice over IP, and Unified Communications (UC) technologies are remaking telephony in a fundamental way that hasn’t been seen since the 1960s. Then the Bell System introduced digital transmission and switching inside the carrier infrastructure to replace analog methods. As digital technology spilled over to businesses through the 1980s, a wave of digital PBX’s replaced older analog PBXs, key systems, and other forms of analog technology. Today the only remnant of analog in the public switched telephone network (PSTN) is the plain old telephone service (POTS) line, the once-universal service. POTS is being discontinued only gradually, but will probably disappear some day as cell phones, fiber to the home, and voice over cable TV networks continue to replace POTS with Voice over IP (VoIP).

1.1 INTRODUCTION TO THE PUBLIC SWITCHED TELEPHONE NETWORK

Telephones are so simple to use that they hide the complexity inside the network that provides the many features we enjoy. In designing a UC deployment, it’s good to understand what UC will replace and extend; that is, what we have used to date.

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FIGURE 1.1 Current loop from CO battery to phone.

Figure 1.1 describes the original telephone technology, the analog phone or POTS line—Bell’s great invention. The phone at the house or office connects to the telco’s central office over a 2-wire ...

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