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CCNA Voice Quick Reference by Michael Valentine

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Understanding Traditional Telephony

This section introduces traditional telephony systems, concepts, and applications.

The PSTN

Figure 5 A Representation of the Public Switched Telephone Network (PSTN)

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The PSTN, or Public Switched Telephone Network, is made up of Central Office switches to which subscriber lines are connected. The CO switch is programmed so that it knows which phone number (subscriber line) is attached to a particular port. If the number called is not on the local switch, the call is routed over an interoffice trunk to another switch, which may have the called subscriber line connected directly to it or may in turn route the ...

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