A method for the time-based accounting of access by users to services provided by a data network, wherein said access by users is provided via at least one primary access node by establishing via said at least one primary access node an always-on connectivity between the users and the network, the method including the steps of: - associating with said at least one primary access node at least one secondary access node configured for acting as a backup node to maintain said connectivity in the case of failure involving said at least one primary access node, said secondary access node including a session manager backup module; - providing an authentication node cooperative with said at least one primary access node and said at least one secondary access node; - issuing from said at least one primary access node a request for credentials for any said user requesting access to said data network, - as a result of receiving valid credentials from said user, said primary access node starting a time-based accounting session for said user by sending an accounting request to the authentication node, - said authentication node sending a first accounting response to said primary access node storing in said primary access node information items concerning said time-based accounting session started for said user, and a second accounting response to said at least one secondary access node storing in said secondary access node information items concerning said time-based accounting session started for said user, - said session manager backup module included in said secondary access node, when receiving said accounting response from said authentication node, creating a single session manager backup (SSMB) instance, concerning said time-based accounting session started for said user, ready for use in case the primary access node fails, and - in the case of failure involving said at least one primary access node having started the time-based accounting session for said user, maintaining said connectivity to the network by re-routing said time-based accounting session for said user towards said secondary access node, wherein the single session manager backup (SSMB) instance of the secondary access node uses the information items concerning said time-based accounting session started for said user of the second accounting response in order to maintain said connectivity. - associating with said at least one primary access node at least one secondary access node configured for acting as a backup node to maintain said connectivity in the case of failure involving said at least one primary access node, said secondary access node including a session manager backup module; - providing an authentication node cooperative with said at least one primary access node and said at least one secondary access node; - issuing from said at least one primary access node a request for credentials for any said user requesting access to said data network, - as a result of receiving valid credentials from said user, said primary access node starting a time-based accounting session for said user by sending an accounting request to the authentication node, - said authentication node sending a first accounting response to said primary access node storing in said primary access node information items concerning said time-based accounting session started for said user, and a second accounting response to said at least one secondary access node storing in said secondary access node information items concerning said time-based accounting session started for said user, a first accounting response to said primary access node storing in said primary access node information items concerning said time-based accounting session started for said user, and a second accounting response to said at least one secondary access node storing in said secondary access node information items concerning said time-based accounting session started for said user, - said session manager backup module included in said secondary access node, when receiving said accounting response from said authentication node, creating a single session manager backup (SSMB) instance, concerning said time-based accounting session started for said user, ready for use in case the primary access node fails, and - in the case of failure involving said at least one primary access node having started the time-based accounting session for said user, maintaining said connectivity to the network by re-routing said time-based accounting session for said user towards said secondary access node, wherein the single session manager backup (SSMB) instance of the secondary access node uses the information items concerning said time-based accounting session started for said user of the second accounting response in order to maintain said connectivity.