Subject: Mobile Communication and Computing

Topic: Mobile Network

Difficulty: Low

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.][1]

Types of Encapsulation Three types of encapsulation protocols are specified for Mobile IP:

1. 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.

2. 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.

3. Generic Routing Encapsulation (GRE): optional. Allows packets of a different protocol suite to be encapsulated by another protocol suite.