ity responds to the trusted Wi-Fi access with the Registration Reply message containing the following fields: MN-NAI, Home Address (HoA), Home Agent Address (HAA) and Lifetime. 18) The trusted Wi-Fi access transfers the Registration Reply message to the mobile that retrieves its HoA. S2c Tunnel Establishment 9.1. MIPv6 mechanism The MIPv6 (Mobile Internet Protocol version 6) mechanism allows a moving host to keep its original IPv6 address, in order to maintain its current session or to be reachable on the move, mobility being managed by the host. The mobile node (MN) is a host that changes network while retaining the home address (HoA) of its home network. When attached to a foreign network, it acquires an additional care-of address (CoA) (Figure 9.1). Foreign network network Agent Mobile Mobile Correspondent Figure 9.1. Components for MIPv6 mechanism Wi-Fi Integration to the 4G Mobile Network, First Edition. André Perez. C ISTE Ltd 2018. Published by ISTE Ltd and John Wiley & Sons, Inc. 166 Wi-Fi Integration to the 4G Mobile Network The home agent (HA) is the entity of the originating network from which the mobile node must register when it attaches to a foreign network. The role of the host agent is to intercept the received packets and send them back in a tunnel to the mobile node. The home agent address (HAA) is that of the interface of the home agent on the home network of the mobile node (Figure 9.1). The correspondent node (CN) is the host that exchanges packets with the mobile node. Its address is noted CNA (Correspondent Node Address) (Figure 9.1). IPv6 mobility implements packet routing optimization between the mobile node and the correspondent node. The systematic routing of the packets exchanged via the home agent is simple to implement. On the other hand, if the mobile node is moving away from its home network and communicating with a correspondent node close to it, then it is more efficient to communicate directly rather than through the home agent. 9.1.1. IPv6 header extensions 9.1.1.1. Mobility ex