G.729 is an ITU-T audio data compression standard that operates at 8 kbit/s using a conjugate-structure algebraic-code-excited linear-prediction (CS-ACELP). This algorithm for voice compresses voice audio in 10 millisecond frames. G.729 is commonly used in in Voice over IP (VoIP) applications because of its inherently low bandwidth requirement. Extensions to the G.729 standard include the following;

• G.729a (G.729 Annex A) - Compatible with G.729 Annex A specifies a coder with several simplifications, including code book search routines. These modifications are known to often result in a slightly lower voice quality.
• G.729b (G.729 Annex B) - Compatible with G.729, Annex B specifies a coder that uses Discontinuous Transmission (DTX), Voice Activity Detection (VAD), and Comfort Noise Generation (CNG) to reduce bandwidth usage. Bandwidth is reduced by preventing the transmission of non-voice during periods of silence.

See G.7xx for more information on how these standards are used in telephony networks.

Enterprise VoIP Planet
The IT Manager's Guide to Voice over IP

ITU Recommendation G.729
Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear prediction (CS-ACELP).

Six Steps to Getting Your Network Ready for Voice over IP
Using low bandwidth CODECs helps reduce bandwidth requirements however due to the overhead of IP, UDP and RTP protocols, such reduction is limited.

The International Telecommunication Union
The International Telecommunication Union is an international organization within which governments and the private sector coordinate global telecom networks and services. This home page offers numerous links to highlights and current topics, standardization, radiocommunication, telecommunication, and general secretariat sectors.

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