Port 1718 H.323 Discovery
Turn your firewall off and test. If you still can't register then something else is wrong. If you can register. Then you know it's a firewall issue.
From IP Office Release 8.0+, the configuration of remote H323 extensions is supported without needing those extensions to be running special VPN firmware.
What release is your system on?
Also, I've referenced this before to get it to work:
1) enable remote worker on the lan port that is used for this
2) set up stun if the IPO is not connected to internet without NAT (NAT -> STUN)
3) enable remote worker on the used extension
4) enable remote worker on the user.
Then on the phone turn off 801.q (important)
Set the external IP address on the phone.
Be sure that these ports are forwarded if the IPO is not on the internet.
1718 UDP
1719 UDP
1720 TCP
RTP ports configured on the LAN port (remote worker part)
ICMP must be enabled for the public IP address used for the remote worker.
Also ,(I've been told this too) close up your RTP range. You're providing capabilities for 2047 handsets to connect. Do you need that many?
"There is one hope, and, as usual, it's Norwegian!"
Professor Farnsworth, Futurama