(1) First perform a ping test to check network connectivity. If supported by the terminal device, it is best to run the ping test directly on the device.
(2) Verify the correctness of the server address, ID, authentication ID and password. You can test the account on a softphone for troubleshooting.
(3) Check if any settings for VPN, VLAN, NAT or ports are required.
(4) Capture and analyze network packets.