How to detect how many connections are there?

[youtian001]

Hi friends,
I run a vncviewer in listen mode on machine A and VNC server on machine B, and use vncconfig on B to connect A. 
So if I run vncconfig twice, I will see two identical VNC window on A.
I want to detect that whether there is already a connection between them. If there is already a connection between these two machines(have already run vncconfig before), vncconfig will not be issued any more.
Anyone has ideal about how to do this?

Best Regards,
Tian