dress Packet source address Packet destination address The foreign agent transfers the packets to the mobile node Packet source address Packet destination address Table 8.2. Data transfer: CN to MN Foreign network network 1 - The correspondent node sends Tunnel Foreign packets to the mobile node. Agent Agent 2 - The home agent establishes the tunnel with the mobile node. 3 - The foreign agent transfers the packets to the mobile node. 4 - The mobile node sends packets Mobile to the correspondent node. Correspondent Figure 8.8. Data transfer In the opposite direction, packets sent by the mobile node are usually delivered directly to the corresponding node, without necessarily passing through the home agent (Figure 8.8). 162 Wi-Fi Integration to the 4G Mobile Network If the mobile node returns to its home network, it unsubscribes with its home agent, by exchanging Registration Request and Registration Reply messages. When the home agent receives and accepts the Registration Request message, it stops providing the ARP proxy function. Upon receipt of the Registration Reply message, the mobile node transmits a gratuitous ARP, showing the correspondence between the data- link layer address of the mobile node and its HoA. 8.3.5. Application to the 4G mobile network The home agent (HA) and foreign agent (FA) functions are hosted, respectively, by the PGW entity and trusted Wi-Fi access. Wi-Fi access server Agent Solicitation Foreign Agent Advertisement Registration Request DIAMETER CCR DIAMETER CCA Registration Request DIAMETER AAR DIAMETER SAR DIAMETER SAA DIAMETER AAA DIAMETER CCR DIAMETER CCA DIAMETER AAR DIAMETER SAR DIAMETER SAA DIAMETER AAA Registration Reply Registration Reply Figure 8.9. S2a tunnel establishment using MIPv4 FA mechanism The procedure for setting up the S2a tunnel, described in Figure 8.9, starts after the mutual authentication procedure for the mobile and the AAA server detailed in Chapter 6. S2a/S2b Tunnel Establishment 1) The mobile transmits the ICMPv4 message Agent Solicitation. 2) Wi-Fi acces