I installed the actual version of 3CX on a XP-system behind a router with build in firewall. I connected 3 GXP-2000 and configured all as shown in the manual. I opened the necessary ports (shown in the manual) and also 10000-20000 in the routers firewall. I disabled the firewall of the XP-system. Also I installed a VOIP-provider (QSC with IPfonie privat). All account informations are filled in 3CX. They only have informations for sip-server and registrar. They don't have (need, they say) a stun-server. I'm now confused: All lines (extensions and VOIP) are showing status "Registered (idle)". In the manual is shown that it should be "on hook" for the extensions. 3CX is registering all (3) VOIP lines every 20 minutes with "... is successful". Now the problems: We are some times not reachable by extern clients/phones. The connection gets lost after some secounds (I think within the process of reregistering the VOIP lines). Sometimes we are not able to call outbound. (Outbound rule with transform mask r for numbers starting with 0 already set automatically in installation process) What do I have to do? Can someone help?