Openfire Roster communication only

I am trying to implement a webchat using Openfire as a server. (at this moment i am using version 4.0.2) and implementing a web client using Strophe.js

I would like to know if there is a way to restrict the communication between users that are in their roster.

Example:

- User Alice have in roster [Charlie]

- User Bob have in roster [Charlie]

- User Charlie have in roster [Alice, Bob]

So the users can only communicate with each ohter are:

Alice + Charlie

Bob + Charlie

But

Alice and Bob cannot talk with each other.

Other important thing would be the roster can only be managed by the administrator

NOTES

I Have already made some experiences and at this moment with Openfire everybody can talk with everybody.

I have the same question in stackoverflow.