Poor Voice Quality on the SCCP Phone - chan-sccp/chan-sccp GitHub Wiki

If a call's voice quality is compromised on the SCCP phone, perform the following tasks as necessary:

• Check the network path for errors, packet drops, loss, loops, and so forth.
• Verify that the ToS level for the media stream being used has been correctly set (through the tos_media parameter in the configuration file).
• Verify that the SCCP phone is plugged into a switch rather than a hub to avoid excessive collisions and packet loss.
• Ensure that there is enough bandwidth on the network for the selected codec (especially for calls over a WAN).
• Determine whether the problem occurs with the handset, headset, or speaker phone, or with all of them.
• Press the i or ? button twice on the phone during the call to view realtime transferring and receiving call statistics.
• Start Collecting the [Call Quality Statistics] to get a better picture.