[asterisk-users] Asterisk as a "gateway"

[Paulo Santos]

Greeting everyone,

I'm trying to connect an old PBX to a Asterisk box with a 4 BRI card. 
The idea is for the PBX to follow asterisk's dialplan rules such as 
calling through VoIP when possible, ISDN when needed, etc, and all 
incoming calls being redirected to the PBX.

The odd part is that incoming calls work perfectly, while when I make a 
call from a phone connected to the PBX through ISDN, I can hear the 
other party but they can't hear me and when the call is made through 
VoIP, I can't ear the ringing nor the other party (neither can the other 
party ear me), but the call is placed.

I'm using alaw codec on every call.

Does anyone have any idea what this problem could be?

Thanks in advance,
Best regards,
Paulo Santos