ses. A half-year trial in the USA gave encouraging but not perfect results. Less reliable are voice recognition and (handwritten) signatures. Mobile phones could use biometry to support e-commerce, most likely using fingerprints. The fact that we cannot change our biometrical identity might be a drawback if the stored identity is stolen. 6.7.2 RADIUS RADIUS is a flexible system, which can be used for many types of authentication services. Its original use was for dial-up connections to companies or to the Internet. The main idea is to protect and/or charge dial-up connections. The building blocks of a RADIUS system can be seen in Figure 6.15. Radius consists basically of a client and a server. The client, who is situated between the modem pool and the server, asks the user for identity and a password. A typical client location is a NAS, which is the access point to the Internet/intranet. The RADIUS server is nothing but a server somewhere in the network. Users are fixed or mobile users accessing the network. See Figure 6.16 and 6.17. End-user authentication in a voice network (PSTN/ISDN/PLMN) interacts with a RADIUS server located at the ISP service network or in a corporate network. For this purpose, the voice network includes a RADIUS client. 6.7.3 DIAMETER Investigations have shown that RADIUS is ill-suited for inter-domain purposes in a roam- ing network Diameter is a new AAA security protocol used with mobile IP. 6.7.4 TRANSPORT LAYER SECURITY (TLS)-SECURE SOCKET LAYER (SSL) The TLS-SSL protocol was developed by Netscape Communications to provide security and privacy over the TCP/IP protocol. Figure 6.13 gives the layer position. The protocol supports server and client authentication. Understanding Changing Telecommunications - Building a Successful Telecom Business Authentication in GPRS Remote authentication dial in user service (RADIUS) RADIUS server Backbone RADIUS client Accept PAP/CHAP / Reject RADIUS server is used primarily for authentication IP address allocation is optional RADIUS server validates 