I'm implementing VoIP environment with remote sites. I need to place some VoIP phones on externally site connected via WAN link with (or not) tunnel between headquarters and branch office. LAN of headquarters is protected by firewall. All phones are configured as internally of 3CX PBX. - Emulate external connection by VoIP phone directly attached to firewall WAN interface communication work fine. - Remote VoIP phones sometimes fail registration to 3CX PBX. - Remote VoIP phones sometimes can establish dialing to other internal phone but communication are dropped after 30 sec. Thanks for all.