I'm using a Zyxel 2602R to connect an extension to my 3CX v8 instance through the internet. This Zyxel device, which is the base modem for Telfort ADSL Internet in The Netherlands, supports SIP, but is very very limited in its settings. It sends out a SIP REGISTER message once in approximately 50 minutes. This interval is not configurable. I noticed the 3CX v8 PBX assumes an extension to be offline when no activity has been received in approxemately 30 minutes. I hoped to resolve the problem by connecting the 3CX PBX directly to the internet with its own public IPv4 address and thus no NAT translation in between, but this did not solve the problem. Is there a way to raise the 30 minute value in 3CX PBX or does somebody have another clever way to make sure the extension will keep registered with 3CX PBX even though its only sending a REGISTER every 50 minutes?