Conflicts between the SIP ALG and the session helper
If you suspect that the SIP session helper is being used instead of the ALG, you can use the
diagnose sys sip command to determine if the SIP session helper is processing SIP sessions. For example, the following command displays the overall status of the SIP sessions being processed by the SIP session helper:
diagnose sys sip status
dialogs: max=32768, used=0
dialog hash by ID: size=2048, used=0, depth=0
dialog hash by RTP: size=2048, used=0, depth=0
mapping hash: size=2048, used=0, depth=0
This command output shows that the session helper is not processing SIP sessions because all of the used and count fields are 0. If any of these fields contains non-zero values then the SIP session helper may be processing SIP sessions.
Also, you can check to see if some ALG-only features are not being applied to all SIP sessions. For example, FortiView pages displays statistics for SIP and SCCP calls processed by the ALG but not for calls processed by the session helper. So if you see fewer calls than expected the session helper may be processing some of them.
Finally, you can check the policy usage and session information dashboard widgets to see if SIP sessions are being accepted by the wrong security policies.