What Is Voice Over Internet Protocol (VOIP)? - Definition & History

Instructor: David Whitsett

David has taught computer applications, computer fundamentals, computer networking, and marketing at the college level. He has a MBA in marketing.

This lesson will define VOIP, explain a little about how the technology works, how it came about, and give some examples of everyday usage. Following this, you'll be able to test your newfound knowledge with a quiz.


If you've ever talked to a friend over Skype, Vonage, or even FaceTime, you have used a form of Voice Over Internet Protocol (VOIP). Voice Over Internet Protocol (VOIP) is a complex technology, but in the simplest terms possible, it means moving voice and multimedia (like video) over networks that were originally designed for moving data (like the Internet). In the past, phone calls typically moved over what is known as the public switched telephone network (PSTN).

To help visualize this, think of the old world as copper wire, phone lines dangling between poles, telephone operators, and switchboards: that's the PSTN. Using Internet Protocol, voice can now be encapsulated (made to look like data packets) and transmitted across the public Internet. Think of the new world as fiber optic cable running underground, higher speeds, and newer technologies.

History and Evolution

This is relatively new technology, first conceived a little over 40 years ago, whereas the technology behind the PSTN (circuit switching) has been around for closer to 100 years. To visualize circuit switching and the way voice had traditionally moved over the PSTN, think of opening up a communications channel between two parties, and during the length of that call, all the conversation went through the same pipe, back and forth. When we hang up, the pipe between us is released to carry something else.

In a packet switched data network (like the Internet), try imagining the network as a shipping warehouse. The words we say are packed up into packages (packets). But there are so many boxes, that they have to be sent out on different trucks to get to the same location. Now it's pretty easy to imagine how this could be really confusing, but it's not because we have shipping labels attached to all these boxes. The boxes can be opened in the correct order on the other end so the conversation comes together at the same place and at the right time, so it makes sense. VOIP equipment (like the gateway in the picture below) and software does the boxing/unboxing of our voice on either end to make this work. The packets are routed correctly through the Internet because of the packet labels, like putting a UPS label on a box and knowing somehow it will get where it is supposed to go.

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