A system for proactively authenticating includes a server having media independent access functions including media independent authentication functions that authenticates other entities attached via an interface to an end of a link specific to a media. A plurality of heterogeneous networks each having media specific access functions including authentication functions corresponding to the other entities attached via the interface to the end of the link specific to the media and mobile devices connected to the plurality of heterogeneous networks, and the server having predefined media independent handover protocols and media independent handover identities based on the media independent functions related to handover, in which the server authenticates candidate access networks prior to the handover of the mobile devices from serving access networks to the candidate access networks each of which belonging to the plurality of heterogeneous access networks having the link specific to the media.