Fi access Wi-Fi Integration to the 4G Mobile Network User plane IP packet 802.11 802.11 Trusted Wi-Fi Access Figure 1.16. Protocol architecture based on S2c interface User plane for trusted Wi-Fi access In the case of untrusted Wi-Fi access, the IPSec tunnel established between the mobile and the ePDG entity protects the S2c interface. The MIPv6 protocol allows IPv6 mobile nodes to move while maintaining accessibility and ongoing sessions. The DSMIPv6 protocol prevents the IPv4/IPv6 dual-stack mobile from running both MIPv4 and MIPv6 mobility protocols simultaneously. The DSMIPv6 protocol also takes into account the case where the mobile moves in a private IPv4 network. The mobile node must be able to communicate with the PGW entity, which acts as a home agent, through a NAT (Network Address Translation) device. In the case of untrusted Wi-Fi access, the S2c tunnel is established from the IP address of the PGW provided by the AAA server during the authentication for the establishment of the SWu tunnel. The mobile can also retrieve the IP address of the PGW entity by querying a DHCP (Dynamic Host Configuration Protocol) server or by performing DNS resolution on the FQDN of the PGW. 1.3. DIAMETER protocol The DIAMETER protocol is used to perform authentication, authorization and accounting functions. Architecture Based on Wi-Fi Access The authentication function makes it possible to control the access of the mobile to the 4G mobile network from a stored secret, on the one hand, in the universal subscriber identity module (USIM) of the universal integrated circuit card (UICC) of the mobile and, on the other hand, in the HSS entity. The authorization function retrieves the service and traffic profile of the mobile stored in the HSS and SPR databases. The accounting function allows generation of events from the PGW entity to the charging entities for the prepaid or postpaid service. 1.3.1. AAA server interfaces The DIAMETER protocol is supported on the interfaces between, on the one hand, the AAA server and, on the ot