[Asterisk-Users] Aastra 9133i and NAT: Can it work?

[Jamie J. Begin]

I've been pulling out my hair all day on this one. If anyone can help,
I'd really appreciate it. :-(

I've got an Aastra 9133i (with the latest firmware version) and a Cisco
7960 sitting behind a NAT device on my LAN. The Asterisk server is
hosted offsite and has a public IP address. 

I've set up port-forwarding on the firewall for both phones to tunnel
the SIP messages initiated by the Asterisk box. It works like a charm
with the Cisco phone by using the following config info: 

voip_control_port: 5077
nat_enable: 1
nat_address: ""
nat_received_processing: 0 

Every time the Cisco phone registers with Asterisk, it does so using
port 5077 and with the corresponding port-forwarding rule added to the
firewall, it works great. However, for the life of me, I can't get the
Aastra to do the same thing. I thought that should be able to do it by
using "sip nat port: 5078" in the Aastra config file, but no dice.
Incoming calls work for about two minutes after the phone is rebooted
and then it loses its registration.

Any suggestions?