No Voice Path

From BGNV Wiki

it is possible for a call to be established but the voice path to be not present. This may be due to a problem with signaling or potentially due to firewall/NAT issues. As signaling often takes a different route to the voice packets, the establishment of a call may ensure that the endpoints can communicate with the signaling server but not necessarily with each other.

One common problem is that signaling may be able to pass through a firewall however, once a call is negotiated, the firewall may not be configured to allow RTP to pass through. This can result in the call being apparently set up although there is no media path. Some signaling protocols include the endpoint's IP address within the signaling message payload - if Network Address Translation (NAT) is used then the packet's IP address will be translated but the IP address embedded in the payload may not.

[edit] Impact

No voice path is present in either direction.

[edit] Resolution

Check the Call Manager/ Gatekeeper/ SIP Proxy for indications of signaling problems. Check the configuration of firewall routers on the voice path. Use a VoIP network analyzer to decode signaling and investigate problem.