Has anybody been able to get incoming calls working in Asterisk on this router? I haven't,

. I'm wondering if it's the router or more likely my own ignorance.
I've forwarded ports to the Asterisk server in the router config. I've told Asterisk to use a small amount of rtp ports, and told the router to forward those to the Asterisk server. I've tried enabling and disabling the rtsp and sip ALG. Is there anything else I should try that I'm unaware of?
A2 with 1.21b2