OBi100, ZyWALL USG50, Callcentric

[lacibaci]

So I have following configuration: OBi100 behind ZyWALL USG50 on Callcentric voip.
All incoming calls get "User not available" message unless I forward port 5060 to OBi.
My firewall configuration is:

Enable SIP ALG                            OFF
Enable SIP Transformations                ON
Enable Configure SIP Inactivity Timeout   ON
SIP Media Inactivity Timeout              120 secs
SIP Signaling Inactivity Timeout          1800 secs
SIP Signaling Port                        5060

I would prefer not to forward port 5060 - Should I change the timeout values to something else?

[lacibaci]

Ok, I figured it out by trial and error. For ZyXEL ZyWALL USG series firewalls (firmware 3.0 and later) you have turn SIP ALG on.  By default, it is off and you will not be able to receive calls.  No other change (port forwarding) was necessary for me.