Pausing Transfers with Winsock! How come ?

I'm building a FTP client and i don't know how pause transfer between the Server and my app with Winsock.
The Server start putting data and never stops, even if i don't use the getdata method.

If i put a Msgbox to ask for stopping, the server still continues putting data in the buffer. Why ?

Does anybody know how pause the transfer while the message is showing without closing and restarting everything ?

Thanks!!!