Firmware version: Any
Create one SIP peer trunk which applied from carrier, the trunk status shows up. But incoming call can not land to PBX, outgoing call from PBX to external number works fine.
Analysis on the PCAP captured on PBX side.
As the following figure indicated, PBX respond "Destination Unreachable" based on the Source port 5060 of PBX and destination port 5060 of carrier.
Actually, the UDP Source port on PBX has been modified with 7788 by client. Which means carrier feedback all the data to 5060 of PBX instead of 7788. So carrier should limited the 5060 port as the only port for data transmission.
Change the UDP Source port to default 5060 on PBX side.