- the n-MAG function transmits the PBU extension containing the identity (MN-ID) of the mobile node and the proxy-CoA of the n-MAG function; - the LMA function transmits the PBA extension containing the LMAA and the HNP; - the n-MAG function transmits the ICMPv6 message Router Advertisement containing the HNP, which allows the mobile to ensure that its IPv6 address is maintained. 8.1.3. Application to the 4G mobile network 8.1.3.1. Trusted Wi-Fi access The LMA and MAG functions are hosted, respectively, by the PGW entity and trusted Wi-Fi access. 152 Wi-Fi Integration to the 4G Mobile Network The GRE (Generic Routing Encapsulation) protocol constructs the S2a tunnel from a key provided by the trusted Wi-Fi access for the downstream traffic and a key provided by the PGW for the traffic in the upstream direction. The procedure for establishing the S2a tunnel is described in Figure 8.4 and corresponds to the auto-configuration of the IPv6 address by the mobile. Wi-Fi access server ICMPv6 Router Solicitation DIAMETER CCR DIAMETER CCA DIAMETER CCR DIAMETER CCA DIAMETER AAR DIAMETER SAR DIAMETER SAA DIAMETER AAA ICMPv6 Router Advertisement Figure 8.4. S2a tunnel establishment using PMIPv6 mechanism The procedure for S2a tunnel establishment starts when the mobile authentication, described in Chapter 6, is successful. 1) The mobile hands over the ICMPv6 message Router Solicitation to retrieve its IPv6 address configuration. This message may contain the access point name (APN) that allows Wi-Fi access to determine the IP address of the PGW. S2a/S2b Tunnel Establishment Otherwise, Wi-Fi access uses the default access point name that is passed by the AAA server during mobile authentication. 2) The Wi-Fi access transmits to the PCRF entity the DIAMETER message CCR (Credit-Control-Request) containing the mobile profile received from the AAA server during the authentication, to obtain the authorization for the opening of the default bearer. The PCRF compares with the rules defined for the network and stored in the SPR (Subscr