bility The mobile node is a host that changes network while retaining the HoA of its home network. When attached to a foreign network, it acquires an additional CoA (Figure 8.7). S2a/S2b Tunnel Establishment Foreign network network Foreign Agent Agent Mobile Mobile Correspondent Figure 8.7. Components of mobility The home agent (HA) is the entity of the originating network to which the mobile node must register when it attaches to a foreign network. The role of the home agent is to intercept the received packets and send them back in a tunnel to the mobile node. The HAA is that of the home agent interface on the home network of the mobile node (Figure 8.7). The foreign agent (FA) is the entity of the network visited by the mobile node. It ends the tunnel and delivers the packets to the mobile node. The foreign agent address (FAA) is the gateway address of the mobile node in the visited network (Figure 8.7). The correspondent node (CN) is the host that exchanges packets with the mobile node. Its address is noted CNA (Correspondent Node Address) (Figure 8.7). 8.3.2. Foreign agent discovery The foreign agent discovery uses ICMPv4 (Internet Control Message Protocol) messages, Router Solicitation and Router Advertisement. The Agent Advertisement message is formed by including an extension, Mobility Agent Advertisement in an ICMPv4 message Router Advertisement. The Agent Advertisement message informs the mobile nodes of the capabilities of the foreign agent and provides the CoA. Wi-Fi Integration to the 4G Mobile Network 8.3.3. Registration Registration allows the mobile node to communicate its CoA to the home agent. If the CoA is obtained from the Agent Advertisement message, registration takes place via the foreign agent. If the CoA is obtained from a DHCP server, and if the R bit of the Agent Advertisement message is set to ZERO, then the mobile node can register directly with the home agent. The registration messages are encapsulated by a UDP header. The number of the destination port (respectively the source port)