How Things Work: Voice over Internet Protocol

When was the last time you tried shopping for a phone card to get in touch with a loved one abroad? As the digital age continues to rise, you can wave goodbye to long distance analog phone calls and turn your attention to a cheaper and easier way of communication. Voice over Internet Protocol, or VoIP, is a method for taking analog audio signals, like the kind you hear when you talk on the phone, and turning them into digital data that can be transmitted over the Internet.

How is this useful? VoIP can turn a standard Internet connection into a way to place free phone calls. The practical upshot of this is that by using some of the free VoIP software that is available to make Internet phone calls, you are bypassing the phone company and its charges entirely.

So how do you get started? There are three ways by which you can make use of VoIP. The most common way is by connecting your standard phone to you computer or your Internet connection using an analog-to-digital converter. This is a very straightforward setup and you’ll be ready to harness VoIP in minutes. IP phones, on the other hand, look just like normal phones, except they connect directly to your router and have all the hardware and software necessary to get started. But the easiest way to use VoIP, especially for students, is through computer-to-computer interactions. All you need is a special type of VoIP software, a microphone, speakers, and a fast Internet connection. Apart from the normal monthly ISP fee, there is usually no charge for computer-to-computer calls, no matter the distance.

Let us take the third case as an example to better understand how VoIP operates. When using a computer to transmit audio, the computer might compress these sounds so that they require less space and will record only a limited frequency range. There are a number of ways to compress audio, the algorithm for which is referred to as a “compressor/de-compressor,” or simply “codec.” Many codecs exist for a variety of applications, such as movies and sound recordings. For VoIP, the codecs are optimized for compressing voice, which significantly reduces the bandwidth used in transferring an uncompressed audio stream.

Once the sound is recorded by the computer and compressed into small samples, the samples are collected together into larger chunks and placed into data packets for transmission over the IP network. This process is referred to as packetization.

Generally, a single IP packet will contain 10 or more milliseconds of audio, with 20 or 30 milliseconds being most common. The packets are then received by the recipient computer, where they go through a similar process to get the audio in a format that can be played by the receiver.

Of course there is much more to VoIP than just sending the audio packets over the Internet. There must also be an agreed protocol for how computers find each other and how information is exchanged in order to allow packets to ultimately flow between the communicating devices. There must also be an agreed format, called the payload format, for the contents of the media packets.

The Forrester Research Group predicts that nearly 5 million U.S. households will have VoIP phone service by the end of 2006. Perhaps the biggest attractions or VoIP for home users are the low price and high flexibility. Also in the works are Wi-Fi IP phones which will allow subscribing callers to make VoIP calls from any Wi-Fi hot spot.

If you’re interested in trying VoIP, a good place to begin is