Can't forward call without using announcement

[lgaetz (Lorne Gaetz)]

This is a symptom of a system behind a NAT router where the media port range is not being explicitly forwarded

SIP Port Forwarding

The nuts and bolts of SIP are complicated, but put simply: SIP session negotiation takes place over the signalling port (default 5060) and the audio (more correctly, the ‘media’) goes over a random pair of ports in the RTP port range (default 10k-20k). It’s quite common for providers to do SIP signalling and SIP media from different hosts, and some providers have many media servers. So imagine what happens when a SIP session is negotiated through a NAT router, but the audio appears from a differ…