T22P delay in placing / answering call

[glamb]

Hi,

We are setting up a 3CX platform and have a Yealink T22P on an external site for testing. The phone provisions and registers fine, but when placing a call from the extension, it takes ~4 seconds for the call to initiate and start ringing. Similarly, if we call the extension on its DDI, the handset starts ringing immediately but when the receiver is picked up, the caller continues to hear the ringing tone for ~4 seconds and then the call is finally connected. Once connected, it works flawlessly with excellent voice quality and no delay, nor do we have any one sided audio.

I've ran the firewall checker and all is fine, I've tried changing the 3CX STUN servers to others and disabling altogether and setting its external IP all to no avail. I've even opened our firewall to allow ALL IP traffic from the external IP of the handsets network.

There are no errors in the 3CX event log nor does the phone report any problems.

The 3CX Client (mobile and desktop) work fine from this external location as do other generic SIP clients.

Any assistance would be appreciated.