VoIP CoDec
Voice over Internet Protocol (VoIP) is a group of communication technologies used to transfer and deliver voice data through IP networks such as the internet. It converts analog audio signals into digital form for transmission and back again into an audio signal for repetition. Internet telephony is a service that utilizes VoIP. When making a call using Internet telephony, the analog voice signal is altered to digital format, which is then compressed into IP packets for transmission via the internet. The entire process is inverted at the recipients end. Internet telephony covers audio, video, fax and text.
VoIP codec
The VoIP codec is the actual algorithm that is used to convert voice data into digital data, compression of the digital data into IP packets to save bandwidth, and decompression of data once it has reached its intended recipient or target location. Codecs perform the conversion by replicating the audio data a few thousand times a second. For example, a G.722 codec samples audio data 16000 times a second. This is known as the sampling rate. Sampling rates differ from codec to codec. Bandwidth usage increases with higher rates of sampling. The most commonly used codec in VoIP is the G.729 which has a sampling rate of 8000 times per second.
The table below lists the available VoIP Codecs.
VoIP Codecs
|
Codec |
Sampling Rate (kHz) |
Bandwidth (kbps) |
License |
|
G.711 |
8 |
64 |
Open source |
|
G.722 |
16 |
48 |
Open source |
|
16 |
56 |
||
|
16 |
64 |
||
|
G.723.1 |
8 |
5.3 |
Proprietary |
|
8 |
6.3 |
||
|
G.726 |
8 |
16 |
Open source |
|
8 |
24 |
||
|
8 |
32 |
||
|
8 |
40 |
||
|
G.728 |
n.a. |
16 |
Open source |
|
G.729 |
8 |
8 |
patented |
|
GSM |
8 |
13 |
Proprietary |
|
iLBC |
n.a. |
13.33 |
Free |
|
n.a. |
15 |
||
|
Speex |
8 |
2.15 – 44.2 |
Open source |
|
16 |
|||
|
32 |
VoIP – a popular choice
VoIP has become quite popular as a result of its low cost advantage, as compared to conventional telephone networks. Calls made between VoIP users are absolutely free; however calls made from VoIP to non-VoIP users incur a gateway subscription based fee. These subscriptions are usually fixed monthly charges.
VoIP is very easy to install and use. Any user with a home PC and broadband connection can install free phone or messaging software and with a headset can start communicating via VoIP. MSN Messenger, ICQ, Yahoo Messenger, and SkyPe are VoIP software that are available as free downloads.