When using Yealink phones, you may experience calls with intermittent one-way audio.
A reboot is required to update your phone's firmware. Unplug your phone and plug it back in to reboot. The firmware install will take about five to ten minutes. Once it is complete, your phone will come back online and will be ready for use.
If you continue to have one-way audio issues after the phone has fully rebooted, disable SIP ALG.
Note: The Yealink T4xG models are still experiencing firmware issues. A solution is being investigated for this phone model. Users with this model should use Virtual Office Desktop or Virtual Office Mobile until the solution is in place.
This is a known issue with Yealink firmware.