s. This interface supports the PMIPv6 (Figures 1.13 and 1.14) or GTPv2 mechanism for the establishment of the S2b tunnel. Control plane 802.11 802.11 Untrusted Wi-Fi Access Figure 1.13. Protocol architecture based on S2b interface Control plane for PMIPv6 mechanism User plane IP packet GRE tunnel 802.11 802.11 IPSec IPSec tunnel Untrusted Wi-Fi Access Figure 1.14. Protocol architecture based on S2b interface User plane for PMIPv6 mechanism The SWu interface is the point of reference between the ePDG entity and the mobile. This interface supports the IPSec (IP Security) mechanism, including IKEv2 (Internet Key Exchange version 2) signaling (Figure 1.13) and the ESP (Encapsulating Security Payload) tunnel of the mobile stream (Figure 1.14). Architecture Based on Wi-Fi Access The construction of the SWu tunnel requires the retrieval of the IP address of the ePDG entity by the mobile. This IP address can be configured in the mobile by various means. The mobile can also perform a DNS resolution on the FQDN of the ePDG entity. The mobile automatically builds the FQDN from the identity of the operator contained in its international mobile subscriber identity (IMSI) or from the tracking area identifier (TAI), where the mobile is located. The construction of the S2b tunnel requires the selection of the PGW entity by the ePDG entity, from information provided by the AAA server during the authentication for the establishment of the SWu tunnel. 1.2.3. Architecture based on the S2c interface The S2c interface is the point of reference between the PGW entity and the mobile. This interface supports the DSMIPv6 (Dual-Stack Mobile IP version 6) mechanism for the establishment of the S2c tunnel built between the mobile and the PGW entity. In the case of trusted Wi-Fi access, this interface supports DSMIPv6 signaling (Figure 1.15) and IP in IP tunnel (Figure 1.16) of the mobile stream. Control plane MIPv6 MIPv6 802.11 802.11 Trusted Wi-Fi Access Figure 1.15. Protocol architecture based on S2c interface Control plane for trusted Wi-