We have a 3CX which we have just setup to receive calls via a voip supplier (voip-unlimited). These calls are fowarded to an extension, which a receptionist answers and then transfers the call onto the relevant person. We are finding that about half of time when the phone rings and the receptionist answers (human receptionist), that the phone is silent with no audio. I have checked the firewall (Draytek Vigor) and the port forwarding seems to be set correctly. Internal extn to extn calls seem ok as do outgoing calls. We are running V6 RC1, one the same subnet as the phones and router. The phones are Grandtream GXP2000. Any suggestions would be very gratefully received. Thanks.