Force Fanvil IP phones to use TCP instead of UDP for SIP registration.

[Matt J - CP]

We recently moved a client's 3CX installation from an onsite server to AWS Lightsail. In doing so, we have encountered a rather annoying issue with UDP not working for SIP registration on the Fanvil handsets. If we switch the handsets to use TCP, all works fine.

We have done extensive testing to determine why UDP is not functioning, but so far, we are at a bit of loss as to what the root cause of the issue is.

What I would really like to know is how we can configure the Fanvil phone provisioning templates to force the use of TCP instead of UDP as the transport protocol. I cannot see any current option in the template that relates to this phone setting. Is anyone aware of an option that can be added to achieve this goal?

Thanks in advance.

 

[JohnS_3CX]

Hi Matt,

If your Fanvils are router-phone models, they might already have a built in SBC.
Read our guides to check your particular model here: https://www.3cx.com/sip-phones/

Otherwise, install a small SBC at the customer's premises which will solve the issue and keep your installation supported and more secure: https://www.3cx.com/docs/3cx-tunnel-session-border-controller/

TCP is just a bandaid, and does not take into account SIP and RTP considerations. It only changes the transmission method to temporarily trick the firewall to allow the traffic through.