How Codecs Make VoIP PossibleBy:Robert Pepper
A VoIP Telephone adapter changes your voice into that data using a “codec,” then sends that data into the phone lines. There are four types of adapters: it can be built into your cable modem, it can be a standalone box, it can connect your phone to a computer, or it can be built into the phone itself. VoIP services usually either charge an ongoing fee for their services and provide the adapter for free, or have you pay a high cost upfront for the adapter, and a low ongoing cost. You can send both audio and video with Voice Over Internet Protocol, but, this article will focus only on audio.
You can make a simple telephone with two cans and a piece of string. The history of the telephone has, in effect, been a matter of making the string longer. Voice Over Internet Protocol works on a completely different principle. Because VoIP is based on the internet, it is based on a series of ones and zeros. A “Codec,” which is short for “Encoder/Decoder,” is hardware or software that encodes your audio --changes it into data-- and then decodes it --changing it back to audio or video-- on the other end. A Codec works by taking a sample of your voice several thousand times a second. This sample rate is measured in Hz (Hertz). A higher sample rate, also known as a bitrate, means better sound quality. One common codec is called “G.729,” and takes 8,000 samples per second; another common codec is called “G.711” and takes 64,000 samples per second. For comparison, a CD takes 44,100 samples per second. In practice, a VoIP signal will sound about the same as a regular phone, or slightly better when connected to another VoIP phone.
The Codec, as I mentioned, changes your voice into data. The Codec can be either hardware or software. If you get your VoIP service from your cable company, they will replace your old modem, and provide you with a VoIP cable modem, which has the codec built in. A popular model is the Motorola Surfboard, which sells for about $90 retail. Many residential and business VoIP providers favor a standalone box. The standalone box has Ethernet input and outputs, so it can be connected to the network before or after the router. One advantage of a standalone box is that you can have two lines, have extra features built in, or make it small and portable. The OOMA Telo, for example, has a speaker for playing your voice mail; the Vonage Box has two lines, each with its own voice mailbox. Internet Protocol (IP) phones are made to take advantage of existing VOIP infrastructure, and are favored by businesses. Some IP phones have power-over-ethernet, Bluetooth compatibility, and WiFi. The more features you want, the more expensive the phone can be. The most expensive phones are more like tablet computers with phones attached. Finally, another way to get VoIP service is to connect a phone to your computer using a USB adapter, or a USB phone or headset. These tend to be inexpensive, with most under $30. Because these adapters only work when your computer is on, it would be more accurate to call them computer accessories than true VoIP adapters.
To review: What makes Voice Over Inter Protocol possible is a Codec, which encodes and decodes audio to data. The codec can be software on your computer, such as Skype, or it can be hardware. A codec processor can be built into your high-speed modem, a standalone box, or directly inside your phone. A VoIP adapter makes it possible to use a Voice Over IP service without giving up your old phone, or, if you choose, to use new phones to stay on the cutting edge of VoIP technology.