ng 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 PAP/CHAP sent from MS and returns access accept/reject PAP = Password identification protocol CHAP = Challenge/Handshake protocol Figure 6.17 RADIUS authentication TLS is application independent, allowing protocols like HTTP, FTP and Telnet to be layered on top of it transparently. The TLS protocol is able to negotiate encryption keys as well as authenticate the server before data is exchanged by the higher level application. The TLS protocol maintains the security and integrity of the transmission channel by using encryption, authentication and message authentication codes. A variety of cryptographic algorithms are supported by TLS-SSL. 6.7.5 WIRELESS TRANSPORT LAYER SECURITY (WTLS) WTLS is based on TLS. As opposed to TLS, WTLS can operate over UDP. The WTLS layer is modular and the application decides what security level and features it will use. Figure 6.13 indicates the layer position. 6.7.6 LIGHTWEIGHT DIRECT