Es empfiehlt sich, folgender Anleitung zu folgen:

How to disable SIP-ALG (SIP Helper) on Fortinet

Open the Fortigate CLI from the dashboard. Enter the following commands in FortiGate’s CLI:

  config system settings
  set sip-helper disable
  set sip-nat-trace disable
  reboot the device

Reopen the FortiGate CLI and enter the following commands (do not enter the text after //)

  config system session-helper
  show // you need to find the entry for SIP, usually 12, but it may vary
  delete 12 // or the number that you identified from the previous command

Create a rule and set it like in the picture above Reboot the device and you should be ready

Disable RTP processing as follows

  config voip profile
  edit default
  config sip
  set rtp disable

Eine Komplette Anleitung zur VoIP Konfiguration für FortiOS 5.6 finden Sie in diesem Dokument: