verse-tunneling by sending the mobile node's packets to the home agent, which forwards them to the communicating node. This mechanism is needed in networks whose gateway routers have ingress filtering enabled, and hence the 2.4 Mobile IP source IP address of the mobile host needs to belong to the subnet of the foreign network; otherwise, the packets would be discarded by the router. The mobile IP protocol defines an authenticated registration procedure through which a mobile node informs its home agent of its care-of address, router discovery (which allows mobile nodes to discover prospective home agent and foreign agents), and the rules for routing packets to and from mobile nodes, including the specification of one mandatory and several optional tunneling mechanisms. Figure 2-5 depicts the protocol stack for IP Convergence Sub-layer (IP CS), i.e., a protocol layer that provides an interface between the IEEE 802.16-2009 MAC with a network layer over the data- plane [12], with routed ASN. Routing over ASN is done using IP-in-IP encapsulation protocols such as generic routing encapsulation (GRE). The GRE is a tunneling protocol that can encapsulate different network layer protocol packet types inside IP tunnels, creating a virtual point-to-point link to routers at remote points over an IP network [26]. IP tunneling is a method of connecting two disjoint IP networks with no native routing path to each other via a communication channel, i.e., the IP tunnel, which uses encapsulation techniques across an intermediate network. In IP tunneling, every IP packet with its source and destination IP network addresses is encapsulated within another packet format native to the transit network. In order to maintain an IP session when the host IP address is changed due to mobility, the Client Mobile IP (CMIP) protocols defined by IETF can be used [27]. The CMIP allows a mobile terminal to maintain its transport connection and to continue to be reachable while moving across a network. The CMIP also provides a common IP layer mobi