The eduroam service uses IEEE 802.1X as the authentication method and a hierarchical system of RADIUS servers. The hierarchy consists of RADIUS servers at the participating institutions, national RADIUS servers run by the National Roaming Operators and regional top-level RADIUS servers for individual world regions. When a user visits a remote institution, the user's mobile device presents their credentials to the local RADIUS server. That RADIUS server discovers that it is not responsible for the realm of the user's home institution and proxies the access request to the national RADIUS server. If the visited institution is in a different country than the home institution, the request is in turn proxied to the regional top-level RADIUS server, and then to the national RADIUS server of the user's home country. That national server forwards the credentials to the home institution, where they are verified. The 'acknowledge' travels back over the proxy-hierarchy to the visited institution and the user is granted access.