Grandstream GXW4216 One way audio internal calls only

[NorthernPC]

I just put a PBX in a small hotel with only 11 rooms, installed a GXW4216 to handle the guest room calls. (I've used the larger versions in bigger hotel builds no issues)

I can call out from the phone to an external number and I get two way audio, I can call in and call one of the extensions and I get two way audio.

But when we call from a phone to the internal phones, we only get audio in one direction from the phone answering the call. all calls to and from the gxw4216 to the office phones, a fanvil x5s and a yealink w60b can't have a conversation.

I'm unable to diagnose this and am hoping someone here might have an idea.

Feel like I should mention, the pbx is hosted. my previous setups were all on premise.

Weirdly the ip showing in the status for the "phone status" is a local IP 192.168.1.237 not the external IP from the ISP. where as the other phones are registering as the external IP.

 

[Saqqara]

How have you configure the phones - sbc, stun or site to site vpn

 

[NorthernPC]

How have you configure the phones - sbc, stun or site to site vpn

I followed the guidelines at https://www.3cx.com/voip-gateways/grandstream-gxw-fxs/

Stun is how I have the other two phones setup and the grandstream gateway should be stun as well. I'm poking around in the configuration now.

 

[NorthernPC]

How have you configure the phones - sbc, stun or site to site vpn

You got it, I looked at the provisioning and, I must have missed the stun setting when configuring the gateway in the pbx. I logged into the gateway and turned stun on, and put stun under NAT traversal.

 

[NorthernPC]

I thought that fixed it, but now there is no audio.

 

[Saqqara]

as the phones are stun, each phone needs

different sip port, rtp ports (block of 19)
fixed it address (either via DHCP or manual)
firewall settup - to port portforward the ports ports to the correct phone ip

 

[Saqqara]

The only supported setup for the 4216 is local lan,

• The device must be local to 3CX, in the same subnet and/or locally routed subnet (including site to site VPN)

 

[NorthernPC]

Installed sbc and issue is resolved.

 

[eddv123]

different sip port, rtp ports (block of 19)
fixed it address (either via DHCP or manual)
firewall settup - to port portforward the ports ports to the correct phone ip

SBC (although un-supported) I would agree would probably solve this as it keeps all the audio local onsite between the endpoints, this can be achieved by pointing the registrar of the gateway to the SBC as I assume you have done.

Although solved for the sake of the ticket I have attached a diagram I have created, that I used for explaining the STUN/Port forwarding scenario to users (it shows the SIP/RTP port split between extensions and how they correlate on the onsite firewall (in this case a Draytek).

The most common mistake on 3CX is when these ports clash between endpoints.