No audio on call pickup of incoming calls


We have a frustrating issue where we intermittently have no audio on call pickup on incoming calls.
We have FreePBX on same LAN as 4 Grandstream GXP2160 phones.
Also have 1 Cisco SPA303.
Issue is present on all phones.
Can upload logs and traces if needed.

I’m guessing this is possibly an RTP issue, perhaps related to my NAT/Firewall settings.
Currently using a Mikrotik router with ports 5060, 10000-20000 allowed and forwarded to FreePBX on LAN IP

Here is flow sequence of affected call from Wireshark.
Can give more info if needed.


On your MikroTik, do you have any “SIP Helpers” enabled? AIP-ALG will cause this type of problem, so if that (or anything like it) is running in the router, you should turn that off.

Thanks for your response Dave.
SIP helper on router is disabled.

However, I think one of our port forwards was set up incorrectly.
Have amended this and seems to be a lot more stable now.

Will keep an eye on it and revisit this if issue arises again.

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