4. Adding New Skills: The Role of Annexes
In the world of technical standards, “Annexes” are official additions or extensions that add new capabilities to the main recommendation. They allow a standard to evolve and improve over time. For G.729, several key annexes have added important new functions.
The table below outlines the most significant ones.
| Annex | Primary Purpose & Key Benefit |
| Annex B | Manages silence more effectively. It provides a silence compression scheme by using a method called Discontinued Transmission (DTX), which saves bandwidth by transmitting very little data when no one is talking. |
| Annex D | Enables operation at a lower bit-rate of 6.4 kbit/s during periods of discontinued transmission (DTX), offering greater bandwidth savings. |
| Annex E | Enables operation at a higher bit-rate of 11.8 kbit/s. This was added because the original standard had no strict requirements for handling music; Annex E provides improved transmission quality for signals like music segments. |
| Annex C+ | Acts as an important reference guide. It defines the proper integration of the main G.729 standard with the functionalities from Annexes B, D, and E into a single, cohesive system. |
These annexes show how standards evolve to become more efficient and capable over time.