A system for the time-based accounting of access by users to services provided by a data network includes a primary access node to provide access by users by establishing via the primary access node a steady connectivity between the users and the network. A secondary access node is associated with the primary access node, such secondary access node being configured for acting as a backup node to maintain connectivity in the case of failure involving the primary access node. The primary access node is configured for issuing a request for credentials for any user requesting access to said data network and, as a result of receiving valid credentials from the user, starts time-based accounting for the user. An authentication node cooperative with the primary access node and the secondary access node stores the secondary access node information items concerning the time-based accounting started for the user. The time-based accounting is thus maintained in the case of failure involving the primary access node as connectivity is maintained by the secondary access node.