Container communication

Hello everyone, I am having trouble with something I hope some flash wizards out there can give me a hand.

Is it possible for an external swf to communicate with the main swf?

Lets say I have a main swf where i have an movieclip playing (lets call is ball_mc) and a container mc and a button to load an external swf. The external swf is a looping movieclip, and somewhere on this timeline i have an actionscript to tell the “main” swf’s ball_mc to stop playing. Now i press the button to load the external swf and it starts playing and when it reaches its actionscript part, the ball stops animating.

This was just a stupid example but i hope you get the idea.

I tried with the _root.ball_mc = stop(); but it doesnt do anything.

Any ideas how i can communicate with the two swfs?