A method for assigning unique identifiers for allowing communication between a GPRS (General Packet Radio Service) system and a RADIUS (Remote Authentication Dial In User Service) server. The method includes connecting one or more external networks to the GPRS system and identifying the or each network with an APN (Access Point Name), and assigning to an or each APN external network a gateway address. An APN-external network authentication request is passed from a GGSN (Gateway GPRS Support Node) to the RADIUS server. The RADIUS server provides to the GGSN upon such request a subscriber IP (Internet Protocol) address to be stored in the GGSN (Gateway GPRS Support Node). The subscriber IP address is unique for the respective APN external network defined in the GGSN. The GGSN combines the APN gateway address and the subscriber IP address to form a unique subscriber identifier; and sends that identifier to the RADIUS server for accounting, e.g., in the form of an ASCII string.