Phone rings but no sound
 

Hi all,

I have introduced a friend to sip and voxalot everything was working fine but now when I call him he answers but there is no sound from his end he says it sounds like an engaged tone and he cant dial out even though he gets a dialing tone.

Anybody any idea what could have changed.

Thanks

What kind of ATA is being used? Is it on a public IP address or behind a NAT router?