 based on the S2b interface The architecture based on the S2b interface corresponds to untrusted Wi- Fi access and network-based mobility. The mobile stream travels through the SWu tunnel, built between the mobile and the evolved packet data gateway (ePDG), and the S2b tunnel, built between the ePDG and PGW entities, to access the PDN (Figure I.6). Wi-Fi Access SWu Tunnel S2b Tunnel GTP-U Mobility / GTP-C Figure I.6. Session establishment - Architecture based on S2b interface The S2b interface supports the PMIPv6 or GTPv2 mechanism for tunnel establishment. The SWu interface supports the IPSec (IP Security) mechanism, including IKEv2 (Internet Key Exchange version 2) signaling and the ESP (Encapsulating Security Payload) tunnel for the mobile stream. I.3.4. Architecture based on the S2c interface The architecture based on the S2c interface corresponds to trusted or untrusted Wi-Fi access and mobile-based mobility. The mobile stream passes through the S2c tunnel built between the mobile and the PGW entity to access the PDN (Figure I.7). In the case of untrusted Wi-Fi access, the S2c tunnel passes through the SWu tunnel built between the mobile and the ePDG entity (Figure I.7). The S2c 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. xxxiv Wi-Fi Integration to the 4G Mobile Network Trusted Wi-Fi Access Wi-Fi Access S2c Tunnel IP over IP DSMIPv6 Untrusted Wi-Fi Access Wi-Fi Access SWu Tunnel S2c Tunnel IP over IP DSMIPv6 Figure I.7. Session establishment - Architecture based on S2c interface In the case of trusted Wi-Fi access, this interface supports DSMIPv6 signaling and the IP tunnel in IP for the mobile stream. In the case of trusted Wi-Fi access, the ESP tunnel, established between the mobile and the ePDG entity, protects the S2c interface. I.3.5. Network discovery and selection Mobile networks are becoming more and more heterogeneous. It is possible for a mobile to be covered simultaneously by differen