I have the exact same problem and stand perplexed. I’m running Spark 2.5.8 and SIP phone v1.0 on Windows XP SP2 with all the latest patches. I double checked that the windows firewall isn’t activated. The only other thing that could interfere with the netwok stack is possible McAfee AV v8.5i
I have moved my workstation into the same subnet/VLAN as our Asterisk server and still see the same results. Note, the Asterisk, OpenFire and workstations are all on the same subnet.
I tcpdumped my workstation and the asterisk server. It seems like all the UDP5060 traffic goes through fine, but the Asterisk server is trying to send packets to my workstation on a random UDP port. My workstation sends back ICMP port unreachable to the Asterisk box.
Note, the Asterisk logs seem to indicate that the call is being set up properly from a SIP perspective.
I don’t think this is a NAT issue. Is there a “debug” mode for the SIP phone plugin in order to help investigate further? I’ll try and capture a full SIP and RTP session for you guys if you think this is useful.