Controlling parent movie clips from external swfs

How is the question when I publish my external swfs obviously I cannot access functions or variables that dont exsist as there is not referance,

so once I load something into a container how to I control the parent and access its functions?

senario = an index - loadeds external content with a sub navigation into a container, I from the externally loaded swf I click something and then something else loads into that container replacing what was initially there.

in as2 this was all very easy but im struggling in as3 can anyone help