Tunnelling and encapsulation
![A tunnel establishes a virtual pipe for data packets between a tunnel entry and a tunnel endpoint. Packets entering a tunnel are forwarded inside the tunnel and leave the tunnel unchanged. Tunneling, i.e., sending a packet through a tunnel is achieved by using encapsulation
Encapsulation is the mechanism of taking a packet consisting of packet header and data and putting it into the data part of a new packet. The reverse operation, taking a packet out of the data part of another packet, is called de-capsulation. Encapsulation and de-capsulation are the operations typically performed when a packet is transferred from a higher protocol layer to a lower layer or from a lower to a higher layer respectively.The HA takes the original packet with the MN as destination, puts it into the data part of a new packet and sets the new IP header so that the packet is routed to the COA.The new header is called outer header.]
Types of Encapsulation Three types of encapsulation protocols are specified for Mobile IP:
IP-in-IP encapsulation: required to be supported. Full IP header added to the original IP packet. The new header contains HA address as source and Care of Address as destination.
Minimal encapsulation: optional. Requires less overhead but requires changes to the original header. Destination address is changed to Care of Address and Source IP address is maintained as is.
Generic Routing Encapsulation (GRE): optional. Allows packets of a different protocol suite to be encapsulated by another protocol suite.