What Is the Difference Between G.711, G.729, and GSM and Why Does the Codec Matter?

What is a Codec?

A Codec is a technical term for the following variations, which essentially mean the same thing: compression – decompression / compressor – decompressor / Code Decode. In practice the compression and decompression is done by a computer program for the purpose of transmitting data over a data connection and allows them to be translated when they reach their destination. Within the telecommunications industry, the data transmitted through the Codec would be the packets of data that make up a call.

In the telephony environment, a codec is sometimes used as a mechanism to maximise bandwidth utilisation by compressing the data of the call and then decompressing it when the call is delivered. For example, there will only be a certain amount of calls that will be able to be transmitted via a 10Gb data link. If you add were to transmit this data using a Codec, then the amount of calls that could transit this link would be greatly increased.


There are two varieties of this Codec, namely U-law and A-Law. U-law is typically utilised within North America and Japan, whilst A-law is typically used by the rest of the world. G.711 will give the best call quality for VoIP on the basis that it uses no compression at all, and as a result, the call quality sounds like using a regular ISDN phone. This Codec is supported by most VoIP providers.


G.729 is considered to offer a good level of call quality at a low bit rate of 8Kbps (kilobits per second), which would mean that you would be able to get more calls through your bandwidth that if you were to use the G.711 Codec. One consideration to make before implementing the G.729 Codec is that whilst is takes up a small amount of bandwidth to transmit the call data, it requires much more CPU processing time to make a call. Therefore, you will find many VoIP phones that are only able to handle one call at a time due to the processing power required to deal with G.729 calls.
The G.729 codec requires a product that does require a user to purchase a licence from an organisation that re-sells licences.


GSM is an acronym of Global System for Mobile Communications, and is the primary communication for mobile phones in Europe.

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