While I am not specifically certain about N600 model router, all new generation routers have inbuilt firewall and recognition and automatic port forwarding enabled for VoIP devices. HT502 is one of the device recognized by routers. I have 3 VoIP ATAs running in Cable Modem->Router->Switch->ATAs and I never experienced any loss of quality with any of the ATAs. Each network setup can be different, I am an experienced person in Network setup and my opinions are based upon my experience only. So yes, other's experience can be different than mine. I guess OP should contact support and they might be able to determine which setup is better for VOIPo service.