Poor voice quality with remote IP phones

In the event that there are remote IP phones that connect to the switchboard from outside the network, the poor quality of the ADSL line can affect the quality of the voice. For this reason it is necessary to set the phone to use G.729 (compressed) codec as a priority and G.711 as secondary.

If you have a gateway you will need to activate the G.729 codec. In the case of the ISDN Mediatrix gateways, enable the G.729 codec in the Media – Codecs section and enter the Editing of the codec details, setting the max size to 20ms. and min. packets and setting the codec voice priority to 1.
KB mediatrix g729

Similarly, set the voice priority of the G.711 codec (aLaw) to 2. This setting is necessary to return the G.711 codec as the primary codec used by the Mediatrix, valid for local terminals, but without it the codec would have priority also for remote telephones.

On remote Polycom IP phones, you can force codec negotiation locally, so that the phone itself dictates the choice of codec. To do this, it is necessary to set the parametervoIpProt.SDP.answer.useLocalPreferences=”1″
Export the phone configuration, write the string indicated among the other parameters (within the <ALL tag), save and load the same configuration file.
For the other IP phones at the moment there are no solutions.