can anybody help me

inçm having problems with my vicidial
when i configure an iax trunk provider i can receive live calls on the agent
screen
but when i put an sip trunk and use the g729 codec i donnt receive live calls and when the customer receive the call and answer it , it hangup automatically
but i use the iax with the ulaw codec it works fine.....
helpme please
when i configure an iax trunk provider i can receive live calls on the agent
screen
but when i put an sip trunk and use the g729 codec i donnt receive live calls and when the customer receive the call and answer it , it hangup automatically
but i use the iax with the ulaw codec it works fine.....
helpme please