Why Axvoice works but Skype does not?

I am using wi-fi internet on a small network of 5 computers in my office. My Axvoice account works fine on this network. However, I get broken voice and poor video quality with my Skype account. It works great when I use it at my home. I can’t understand why Axvoice SIP account works but Skype does not? As far as I know both are using the same technology.