The CM is responsible for managing user participation in a Collaborative session and for integrating the resources of VRV and VCS.Users can request the coordination role to the current coordinator , who can accept or reject the request ,generating a visual feedback to the requestor. Upon the occurrence of a "change coordinator " event in a CEE collaborative session,all users are notified by the awareness mechanism. At any time,the user can disconnect from the session to do private work,and reconnect later.Then,the user's state is resynchronized with the state of the session,which is controlled by the CM service.