Avaya 555-245-600 manual Codecs, Echo and Signal Levels, Tone Levels

Codecs

Echo and Signal Levels

As mentioned before, in circuit-switched telephony, echo may be caused by acoustic reflection in the remote party's environment, or by electrical reflection from 2-to-4 wire analog hybrid impedance mismatches. Impedance mismatch can occur in analog telephones and analog line/ trunk cards, electrical cross-talk in circuitry, or in telephony wiring (particularly in low-cost headsets). For this reason, in circuit-switched analog and digital phones, a relatively large transmit loss is implemented in order to minimize the perceived echo due to electrical reflection and cross-talk effects. In principle, the transmit loss of telephones could be made very large followed by signal amplification in the receiving telephone. In practice however, the transmit loss should be limited to prevent the electrical voice signal from dropping below electrical background noise. This has resulted in the adoption of transmit loss and receive loss values around 8 dB and 2 dB, respectively, although country-specific values may actually deviate quite significantly from these values.

The loss plan administration provided by Avaya Communication Manager software is primarily intended to control signal losses in telephones and gateways, and not intended to control echo. However, in case of severe echo, the administered loss can be changed to a different plan. In general, an increase of the loss between two endpoints by a certain amount will decrease the echo level by twice this amount. It is not advised to use loss plan administration in this way without consultation with Avaya Services personnel. It is better to reduce the echo by using Avaya products with echo cancellers to minimize echo.

Tone Levels

The level of call progress and DTMF tones played out through telephones must adhere to specified levels in order to be satisfying for the average user. Again, respective standards are country specific and can be set in Communication Manager by administration. The volume of received call progress tones can be adjusted by the telephone volume control.

Codecs

Codecs (Coder-Decoders) convert between analog voice signals and digital signals. Avaya supports several different codecs offering varying bandwidth usage and voice quality, including the following codecs:

●G.711 produces uncompressed audio at 64 kbps

●G.729 produces compressed audio at 8 kbps

●G.723.1 produces compressed audio at 5.3 or 6.3 kbps

●G.722 produces compressed audio at 64, 56, or 48 kbps

Issue 6 January 2008 251