First I went to the Global SIP screen and set things up in the usual way so that the phone had the information needed to register to the PBX, etc.
This would work great if the phone could route directly to the PBX and back again but with Network Address Translation occurring on my end throws a monkey wrench into the works when it comes to SIP and RTP.
So in the end it seemed necessary to take a look at the available settings on the 2Wire device and see what my options were. There weren’t many.
I ended up explicitly allowing the UDP ports that the phone uses. On the Uverse gateway. Here are the steps:
First I went to the Firewall tab and then Firewall Settings. I selected the phone from the Computer drop down and selected “Allow individual application(s)” like so.
Next, I clicked Add a new user-defined application and created a user-defined app as below.
The phone sends and receives RTP traffic on ports beginning with UDP 3000. I opened up ten ports allowing for five simultaneous calls. This seemed like more than enough for my purposes.
When I was done I clicked “Add Definition” and then the new user-defined app was ready to go. I Selected it on the following page, clicked Add, and then Done. After that the phone worked great.
What I did find odd is that I didn’t need to define a stun server on this phone to get it to work in this situation. The 2Wire residential gateway must do some sort of manipulation of SIP packets because from what I could tell all of the fields looked correct with the appropriate public IPs in the right places.
Enjoy!
Matt