文档介绍：How IP Telephony Works
by Jeff Tyson
If you regularly make long-distance phone calls, chances are you've already used IP telephony
without even knowing it. IP telephony, known in the industry as Voice-over IP (VoIP), is the
transmission of telephone calls over a work like one of the works that make up
the . While you probably have heard of VoIP, what you may not know is that many
traditional panies are already using it in the connections between their regional
offices.
This person is using puter to talk to a friend in another state.
In this article, you'll learn about VoIP and the technology that makes it possible. We'll talk about
VoIP's major protocols, about the various services provided and the low-cost, often free software
that allows you to take advantage of them.
But first, let's discuss the fundamental problem with existing works -- namely, their
reliance on circuit switching.
Circuit Switching
Circuit switching is a very basic concept that has been used by works for over 100
years. What happens is that when a call is made between two parties, the connection is
maintained for the entire duration of the call. Because you are connecting two points in both
directions, the connection is called a circuit. This is the foundation of the Public Switched
work (PSTN).
Click "Play" to see how circuit switching works.
Here's how a typical