VoIP technology provides a way to send an analog signal (the sound of your voice) over a digital medium - the Internet. In order to understand how this process works, we can use a simple real-world example. Let's say that you have VoIP service and a traditional analog telephone. Your telephone is connected to your high-speed internet connection using an analog telephone adapter (or ATA). We will trace what happens when you place a call from that phone to someone in another city, what would normally be a long-distance call. We will also assume the person you are calling has only regular analog phone service, with no VoIP capability. By the way, this process is the same if you are using a PC softphone, just that the PC performs all of the functions of the ATA.

When you pick up your phone and dial the number, the ATA converts the analog touch-tones into digital form. The resulting digital phone number is sent by the ATA to the VoIP service provider's routing system, which itself is on the internet. This routing system looks at the number to determine the location the call is going to and routes the call to the PSTN (or Public Switched Telephone Network) at that location (which causes the other person's phone to ring). Once the call begins, an analog-to-digital converter in the ATA converts the sound of your voice into digital packets that can be split up and sent over the Internet.

On the other end, where your VoIP service connects to the PSTN (via the Internet), these digital packets are converted back into an analog signal that goes to the person you have called. The sound of their voice goes through a similar process, but in reverse. It is converted from analog to digital at the point where the PSTN is connected to the Internet, and is then sent in the form of digital packets to your ATA. Your ATA then converts these digital packets back into an analog signal to provide the voice that you hear on your telephone receiver.

So there are two basic components to the VoIP technology - the analog-to-digital conversion, and the protocol (the “P” in VoIP) that facilitates transmission of the digital packets over the Internet. Analog-to-digital conversion has been around since the first days of digital electronics. This technology is built into the sound card on your PC - if you play a CD on your PC, an analog-to-digital converter on your sound card converts the digital data on the CD to the analog signal required by your computer speakers.

The other component, the protocol, is fairly recent. The inventors of VoIP designed a protocol (actually there are several similar ones in use today) that is optimized to transmit digital voice data over the Internet and reassemble it at the other end. A special protocol was needed to do this because of the continuous nature of a voice transmission - there could be no gaps or pauses in the data stream. The result is a protocol that can provide sound quality over the Internet that is at least as good as, and in some cases better than that of the regular telephone networks.

If you use a PC softphone (basically a piece of software that turns your pc into a telephone) to make VoIP calls, you are using the sound card in much the same way. If you are using an analog telephone adapter for VoIP calls, then this adapter has the necessary analog-to-digital hardware incorporated into it. These adapters, like many of the digital devices we use, are actually small, dedicated PCs. Also, some phones are now being manufactured that have the ATA built into them. These phones act like regular analog telephones, but can be plugged directly into your high speed Internet modem or router.

Although this discussion has been as non-technical as possible, you can still see that VoIP is a sophisticated technology. VoIP provides a good example of using a newer technology to greatly enhance an existing one.

This article "How Does VoIP Work" is Copyright 2006 Compare-VoIP.net and may not be reproduced.

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