Poor Voice Quality with Remote IP phone

If user who is connected remotely to PBX and experiencing voice quality issue due to poor bandwidth of ADSL line (bandwidth is not sufficient), you can improve this by saving the bandwidth: saving G.729 (compressed) as priority codec and G.711 as secondary codec. You should also change the codec priority on the connected gateway as well. If you are using a Mediatrix gateway as ISDN then you can select the G.729 codec by going to Media  Codecs. Then enter the following details under the G.729 section:

    • Set the Voice Priority to 1.

Set Minimum Packetization Time to 20ms.

  • Set Maximum Packetization Time to 20ms.

We advise that you set the G.711 codec (a law) as secondary codec as this codec will be used by the Mediatrix as primary codec for the local users. If you do not set the secondary codec as G.711 then Mediatrix will use G.729 for local users too. You can force the remote IP phones to use the primary codec by configuring the parameters below in the config fie of the phone.

VOIPPROT.SDP.ANSWER.USELOCALPREFERENCES = “1”

Please see below for the steps required to add parameters in the config file:

  • Access the web interface of the phone as admin user.
  • Go to Utilities  Import/Export Configuration.
  • Click on Export all configurations (except Device Settings).
  • Open the fie with text editor (e.g. Notepad++).
  • Got to node All and add below line:
  • voIpProt.SDP.answer.useLocalPreferences = “1”
  • Save the file and import it from the Import Configuration file field.
  • Once you import the file then phone will reboot.
  • After the reboot number will be dialled as soon as you lift the handset, press the speakerphone or Line1 Key from the phone.
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