[Freeswitch-users] There is no voice in Two party call

Hi I am a student and I want work on freeswitch. I have read freeSwitch documents (introduction, how to install, use default confuguration,...). for start of using freeswitch, I make three computer network together with a hub, after that,I install freeswitch on one of them and X-Lite on another computers, network checked with sharing file and ping issue. After registering of two X-lite phone with No. 1001,1002, they can call each other but there is no voice !!! :( I am not able to find what's the problem. it is very important to me please help me. thank you.