Step 1:TE desktop can call TE30,from this we can infer that the network is ok;and also there is no firewall in the network,so it is not the issue of network;
Step 2:When TE30 call the number of TE desktop,it is ok,
Step 3:Check the port of TE desktop,it is 5060,it is normal;
Step 4:Confirm the transmission mode is UDP or TLS,and confirm with R&D,the TLS can not support IP call.
Change transmission type into UDP.then the call is successful