Issue on VoIP inbound and outbond calls on SSL VPN

[jjpoyaoan]

Hi,

I am having some weird issues with our VoIP users which all uses Forticlient going to our Fortigate via SSL VPN then to another router where the VoIP server sits in. Here is the issue when user1 answers an inbound call, user1 will not receive the call instead user2 will pick up the call without him knowing. Same goes with outbound calls when user1 tries to make a call, the call will suddenly stops and it will again transfer to another user. The weird part is if there is only 1 user inside the SSL VPN network that user will be able to make outbound and inbound calls. 

Not sure if this is made by the NAT, when VoIP is going to SSL VPN users it might be unable to direct calls.

I tried disabling the NAT from the policy of Fortigate which was mistake that prevented the users from connecting to the VoIP server and also the internet. Since as per my colleagues they suspect the NAT in the Fortigate which causes the issue.

My Question is, Is there a way I can disable the NAT in the firewall rule from the Fortigate while maintaining the SSL VPN connection to the LAN?

Thanks in advance.

Jonas