BusinessPhone Communication Platform 5.1
Dialogs

## Voice Transmission Quality Tables

In order to keep the required bandwidth for a Voice-over-IP call as low as possible, voice codes on the IPU are used to compress the used telephony bandwidth of 64kbit/s to a lower value. However, each compression causes a reduction in the voice transmission quality.

To access the Voice Transmission Quality dialog, open the “System” menu in the Configuration directory tree. Then open the “System parameters” submenu and click on “General IP data” to open the context menu. Now select “Voice transmission quality” from the context menu.

The VTQ tables show the default order of the codecs:

2165 |  | Voice transmission quality table 1

2166 |  | Voice transmission quality table 2

2167 |  | Voice transmission quality table 3

2168 |  | Voice transmission quality table 4

For more information about a field or a setting, click on the command link in brackets.

### Supported Voice Codecs

ASB 150 02 supports the following voice codecs:

- G.711 provides uncompressed voice transmission, and nearly the same voice quality as a circuit- switched line.
- G.729 Annex A (with Annex B) provides compressed voice transmission (8 kbit/s). The advantage of this codec is that the compression rate is down to 8 kbit/s, while the speech quality is on a very high level (comparable G.711)
- G.723.1 provides compressed voice transmission (6,4 kbit/s) with some reductions in the voice quality, however it occupies less bandwidth.

### Transmission Quality Levels

The system is prepared for 4 different transmission quality levels (command 2165-2168), which can be defined on extension level for outgoing Trunk IP-Gateway calls as well as for calls to and from an IP-Extension. Each level comprises a set of 5 voice codecs, whereby the access of the codecs depends on a different order of priority. You can define the codec priority using the four tables of the Voice Transmission Quality (VTQ) dialog.

Note

A codec can be included only once in a table.The H.323 standard does not clearly define, how an IP-Extension can be forced to use a codec which the system proposes. This unclear situation in the standard might result in the use of different voice codecs for each speech direction. In order to avoid such a situation, it is recommended to define one voice transmission quality table which only contains one codec for all five priorities. By using this way of programming, it is secured that one and the same codec is used for both speech directions. If the IP-Extension does not support this codec, no calls can be set up.

#### Actions

Submit |  | To set the changed parameters. |
Reload |  | To reload the current parameters. |

Revision: B © Ericsson Enterprise 2003