, security and individuality. Mobile commerce is a big driver for security functions in the terminals for authentica- tion and cryptography. Tunnelling In GPRS and WCDMA/UMTS one of the main protection methods is to send end user data in tunnels. GPRS and WCDMA/UMTS use tunnels for signalling and user data traffic. The pro- tocols are called GPRS tunnelling protocol - user (GTP-U) and GPRS tunnelling proto- col - control (GTP-C). GPRS tunnelling protocol (GTP) is used in the internal backbone. If required, IPSec can be used internally as well. See Figure 6.28. Tunnelling towards external networks will only be performed if the interworking case SO requires. The media gateway and the GGSN are the tunnel end points for the GTP-U for packet mode communication. The GGSN tunnel end point is situated on the border between the basic WCDMA/UMTS core network and the ISP's point-of-presence (POP). Destination/source private IP addresses Application server Corp. network GTP tunnel IPSec tunnel Backbone GGSN/FW public IP addresses Figure 6.28 Packet routing and tunnelling Understanding Changing Telecommunications - Building a Successful Telecom Business The SGSN (serving GPRS support node) supports the GTP-C protocol for control sig- nalling between SGSN servers and GGSN. GTP-C is transported by UDP/IP and contains functionality for SGSN media gateway function - GGSN tunnel management and control. GTP-C protocol for control signalling between SGSN servers and GGSN supports end- user authentication interacting with a RADIUS server located at the ISP service network or in a corporate network. For this purpose, the GGSN includes a RADIUS client. The optional IPsec function makes it possible to have secure transfer between SGSN and GGSN nodes and between GGSN and external networks. The IPsec may also be used to secure the link between the GGSN node and the network management terminal. The security function also includes the packet filtering options in order to protect against intrusion or denial of service attacks. 6.14.3 E-COMME