How to communicate between external SWF please?

Hello,

I got a new question regarding a project I’m doing.
I’m creating a website template which has a navigation with links and 2 zones dedicated to load external contents.

Loading 2 external swf by clicking on a link is no problem but my question is :
I would like one of my external swf to contains links which could again reload external swf in the same two zones.
How can I do that ? I’m working with document classes. Maybe it helps… ?

A little example :

ZONE A ---------- ZONE B
EXT SWF EXT ---- SWF WITH LINKS IN IT THAT RELOADS ANOTHER SWF IN
ZONE A ---------- ZONE B

Many thanks !!