Issue with One-way audio/dropped calls from remote site

[Mint Julep]

Running 3CX PBX version 12 SP version 6.1 behind a SonicWall NSA2400 firewall. We have a remote site using a MicroTik RB2011 firewall (RouterOS 6.37.4) that's configured for port forwarding to the static WAN IP where the PBX resides. 3CX SBC version 12 runs on a dedicated proxy server for all Yealink handsets and wireless base stations at this remote site. 3CX soft phones connect directly to the static WAN IP of the PBX.

On the MicroTik under filter rules, ports that are forwarded to the static WAN IP of the PBX are:
TCP: 5000, 5001, 5060, 5090
UDP: 5060, 5090, 9000 - 9255

We have no NAT rules in place for any of these ports. SIP/ALG is disabled on the MicroTik

We are masquerading VoIP traffic out a specific interface on the MicroTik that passes VoIP traffic via dedicated circuit to the PBX location. We have a separate interface that connects to a different ISP for general web traffic.

Behaviors we're seeing are:

1. Between 30 seconds - 2 minutes into a call, static is heard on the line and call then drops.
   
   
2. On Yealink handsets, users notice a message that "no tunnel connection" appears on the phone's LED display and they have to wait a few minutes before being able to call out. Users occasionally notice a "user not found" message on the Yealink LED display. These phones are on the same LAN as the Proxy server
   
   
3. On the soft phones, users report call quality starts OK but becomes garbled during the conversation. Occasionally, when requesting a phone number from a caller, the audio stream will elongate a single number (i.e., 4 is heard as “ffffffffffffff”).

Please review and let me know if you can provide some insight on how to correct these chronic audio issues.

Thanks!

Mint

 

[Mint Julep]

Additional note: 3CX firewall checker at PBX location ran successfully as did the 3CX web firewall checker utility at our remote location.

 

[YiannisH_3CX]

Hello @Mint Julep

I would recommend upgrading your PBX to V15.5 where significant improvements have been made to the way the phone system handles remote extensions. The PBX also supports newer firmware versions for IP phones which include bug various bug fixes that can help you eliminate such issues.