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Online! The Book by Wendy Taylor, Chris Pirillo, John C. Dvorak

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How Does VoIP Work?

It's simple: Voice becomes another data application running over the IP network. The PBX becomes a large server.

Technically, a VoIP call takes place in the following way:

A user picks up the handset, which signals an off-hook condition to the signaling application portion of the VoIP in the network. Then the session application portion of VoIP issues a dialtone and waits for the remote client to dial the number. When a number is dialed, the numbers are stored by the session application. After a sufficient number of digits are accumulated, the number is mapped to an IP host through the dial plan mapper. The IP host has a direct connection to either the destination telephone number or a PBX to complete the call.

Next, the H.323 ...

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