establishment of the S2a tunnel. The construction of S2a tunnel requires the selection of the PGW entity by Wi-Fi access, from information provided by the AAA server during authentication. This information can be the IP address of the PGW entity, the full qualified domain name (FQDN) or the APN. Trusted Wi-Fi access retrieves the IP address of the PGW entity by performing DNS (Domain Name System) resolution on the FQDN or APN. 1.2.1.1. PMIPv6 mechanism The PMIPv6 (Proxy Mobile IP version 6) mechanism relies on the signaling provided by the mobility extension of the IPv6 header exchanged between Wi-Fi access and the PGW entity (Figure 1.7) and on the GRE (Generic Routing Encapsulation) tunnel of the mobile stream (Figure 1.8). Control plane Mobility Extension of IPv6 header Trusted Wi-Fi Access Figure 1.7. Protocol architecture based on S2a interface Control plane for PMIPv6 mechanism Architecture Based on Wi-Fi Access User plane IP packet 802.11 802.11 GRE Tunnel Trusted Wi-Fi Access Figure 1.8. Protocol architecture based on S2a interface User plane for PMIPv6 mechanism The MIPv6 mechanism requires functionality in the IPv6 stack of a mobile node. The exchange of signaling messages between the mobile node and the home network agent makes it possible to create and maintain a correspondence between its address in the home network and the foreign network. Network-based mobility supports the mobility of IPv6 nodes without mobile involvement by extending MIPv6 signaling between the TWAG function and the PGW entity. This approach to support mobility does not require the mobile node to be involved in the exchange of signaling messages. The PMIPv6 protocol is an extension of the MIPv6 protocol. A mobile node can operate in an IPv4, IPv6 or IPv4/IPv6 environment. The PMIPv6 protocol independently supports the mobility of the IPv4 address and the transport of IP packets in an IPv4 network. 1.2.1.2. MIPv4 mechanism The MIPv4 FA (Mobile IP version 4 Foreign Agent) mechanism is based on MIPv4 signaling (Figure 1.9) and the I