I wonder if someone out there is smart enough to help me with the problem I've got:
We use a routed Mikrotik network that has 12 hops from point A to B using several ADSL routers and one dedicated VOIP router. At point B I have several Asterisk based PBXs and some standalone IP phones. I can setup all of these devices to make perfect outbound calls. I can get all of the PBXs to receive incoming calls using the NAT=yes setting in my Asterisk trunk settings.
My problem lies in my stand alone devices. I use Snom, Grandstream and Siemens phones. The Grandstream phones are fine with incoming calls. Some of the Snom phones are fine. None of the Siemens are fine - except when I enabled SIP ALG on my main VOIP router. Then ALL of my stand alone SIP devices can receive incoming calls. However then some of my PBX's don't register - they report "Request sent" when I do a sip show registry. When I check the SIP trace on my standalone device (usually Snom 300) it shows that it does receive the call but that it doesn't accept the invite. Probably due to the wrong port or IP address. The phones that can receive incoming calls do so on the same port the registration was sent out on. The phones are all registered at our VOIP service provider so thats also not it
What I have tried:
1) Turning Upnp on at the source ADSL voip router
2) Turning Upnp on at the customer router
3) Turning Upnp off everywhere
4) Turning SIP Alg off and on
5) Turning SIP helper off and on
6) Change the SIP port and RTP port on the standalone devices that can't receive incoming calls to something other than 5060.
7) Turned "Support broken registrar" on on the Snom 300
The problem is that because we only have one VOIP router I can't do port forwarding and can't assign static IP's
Any suggestions? This is a really big headache and keeping me back from more implementations. If anyone can help I'll gladly provide assistance to you for any of your problems.