[Blink] Receiving Blink callee drops call because no answer acknowledgement sent from caller

[Zoho]

Hello Blink support forum,

I am testing a basic Kamailio SIP server used with RTP-Engine behind an edge router facing the internet. I am initially testing with two client UAs in the same LAN network*behind* the router firewall, with the Kamailio server in a separate LAN network (also behind the router firewall). SIP requests (and RTP media intended for assigned UDP ports) received by the edge router (UAs are configured using the public ip domain name) are port forwarded to the SIP server. The two LAN networks behind the edge router are not firewalled from each other--i.e., you can ping across the LANs.

I am able to establish registration with Blink soft phones, but have a problem with the RTP media connection. The initiating Blink UA caller starts the media proxy as soon as the receiving Blink UA accepts the call, indicated by the call timer starting. But after accepting the call the receiving UA's timer doesn't start and after 10-15 secs hangs up with a NO ACK error message. The initiating UA caller does not send back the final ACK even though it has received the callee's answering 200 OK.

I am able to establish call connections using the same setup described above using Jitsi or MicroSIP, but not Blink. I like the Blink features and would like to make it work. Any advice is appreciated.

Thanks,

Steve
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