I'm facing a strange issue, I have a Cisco 2800NM Series router (2821) that has an FXS PVDM voice card configured with default configuration in the voice ports, when i try to make an intra call between two extension inside the same router the caller don't hear that the phone is ringing in the other side but it is in fact ringing in called extension. but when i make an inter call with another router or a PBX the caller hear the ring tone.
Can you please help me on that, I have tried different analogue phones and always the same problem.
find attached a part of the configuration that is made on the router.
Note : i have the same configuration in other similar routers and it works fine.