Synchronizing VoIP sessions requires the FortiGates to automatically allow RTP sessions created by a previous SIP session even if the SIP session was received by a different FortiGate. FortiOS calls these created sessions expectation sessions and synchronizing VoIP sessions requires expectation session synchronization.
diagnose sys session list expectation command on each FortiGate to display the synchronization state of expectation sessions.
Enter the following commands on each FortiGate to synchronize expectation sessions to support VoIP. You must enable TCP session synchronization to synchronize other types of sessions.
config system ha
set session-pickup enable
set session-pickup-expectation enable