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■    Public Switched Telephone Network (PSTN, also called plain old telephone services, or POTS)

■    Integrated Services Digital Network (ISDN)

■    Other digital connection methods (including one of the digital subscriber lines, or DSLs, and T-series connections)

The Public Switched Telephone Network (PSTN)

Almost everyone outside the phone companies refers to PSTN as POTS. This is the wiring system that runs from your house to the rest of the world. It is the most popular method for connecting a remote user to a local network because of its low cost, ease of installation, and simplicity.

Even the employees of most phone companies refer to PSTN as POTS when discussing work inside the phone company. The only time the acronym PSTN is used is when making a technical presentation or when a phone company’s marketing department is making a public statement.

Attributes of PSTN

Two key concepts when discussing PSTN are public and switched. Public, of course, is the opposite of private and means that, for a fee, anyone can lease the use of the network, without the need to run cabling. The term switched explains how the phone system works. Although one or more wires

are connected to your home and/or office, they are not always in use. In effect, your wiring and equipment is offline, or not part of the network. Yet, in this offline state, you have a standing reservation so that you can join at almost any time. Your identification for this reservation is your phone number, which is what makes the phone companies a viable communications network. You initiate a connection by dialing a phone number. Can you see how it would be technically impractical if every phone number were connected all the time? The cabling issues would be almost impossible.

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