Hi all,
I have a problem with Asterisk connection. My configuration is this: I have a server Asterisk (A) that is connected with another server Asterisk (B), and the last one in connected to SELTA’s telephone exchange ©.
The problems is: when with a IP-phone connected to the server A, I call the telephone exchange C (the connection in this way is: A --> B --> C --> B --> A), I CAN’ T hear the “free ring sound” on my receiver (sound schould be: tuuuuuu … tuuuuuu … etc), but I hear nothing, however the phone that I called rings!
Instead when I call a IP-phone connected to server B, with a IP-phone connected to server A (the connection in this way il this A --> B --> A), I CAN hear the “free ring sound” on my receiver!
Again when I call telephone exchange C with a IP-phone connected to server B (the connection in this way il B --> C --> B), I CAN hear a beautifull “free ring sound” on my receiver!!! 
At the end, when I call from telephone exchange C to A or to B asterisk server, I CAN hear “free ring sound” on my receiver.
My question is… why the connection from A to C not work perfectly as all other connection??? What can I do to solve this problem? 
Thanks a lot…
Ciao a tutti… 
Andrew