An apparatus configured to operate as a Backup system in a Data Layered Architecture Public Land Mobile Network. The apparatus comprises an interface for enabling a data exchange between the apparatus and a plurality of Authentication Centre Front Ends, and a memory for storing subscriber authentication data. The apparatus further comprises a processor for detecting a failure of a Data Back End and for receiving a redirected authentication data set request from an Authentication Centre Front End via the interface. The processor is further configured, in the event of a detected failure of Data Back End, to generate one or more authentication data sets in response to the request using the data stored in the memory, and send the generated data set(s) to the Authentication Centre Front End via the interface.