This question appears in Mumbai University > Mobile Communication and Computing subject

Marks: 10M

Year: May 2015

The Mobile Node is a device such as a cell phone, personal digital assistant, or laptop whose software enables network roaming capabilities.

The Home Agent is a router on the home network serving as the anchor point for communication with the Mobile Node.

The Foreign Agent is a router that may function as the point of attachment for the Mobile Node when it roams to a foreign network, delivering packets from the Home Agent to the Mobile Node.

Why tunnelling?

• Consider a situation when a Correspondent Node (CN) wants to send an IP packet to a Mobile Node (MN). All the CN knows about this MN is its IP address.

• The CN is totally unaware of the MN’s location. (Which in fact is a major requirement of Mobile IP) and so sends it as usual to MN’s IP address.

• The internet routes this packet to the Home router of the MN also called as Home Agent (HA).

• The HA now knowing that the MN is not in its home network send encapsulates and tunnels it to the COA.

• The Care-of-address (COA) defines the current location of the MN from an IP point of view (e.g. when a person Mr. XYZ stays as a guest in someone else’s home , the letters he receive will be marked as Mr. XYZ ,C/O i.e. care-of Mr. ABC)

• Since internet routes are created based on the header contents of an IP packet, to route it from HA to COA, we need a new to create header for the packet to be transmitted.

• The new header on top of the original header is made (refer diagram-2). Now this will enable us to set a new direct route (a tunnel) to the MN from the HA as it is roaming.

• Tunnelling: It is the process of creating a tunnel by the HA to the COA to route packets to the Mobile Node as it roams.

• It establishes a pipe (a data stream between two connected ends) wherein the data is inserted and moves in FIFO order

• Encapsulation: Tunnelling has two primary functions: encapsulation of the data packet to reach the tunnel endpoint, and decapsulation when the packet is delivered at that endpoint.

• The default tunnel mode is IP Encapsulation within IP Encapsulation. Optionally, GRE and minimal encapsulation within IP may be used. Let us study minimal encapsulation technique.

• Minimal encapsulation is an optional encapsulation method for mobile IP.

• In methods like IP-in-IP encapsulation fields are redundant. So, here the number of fields is reduced with affecting the transmission.

• No field for fragmentation offset is present in inner header

• Minimal encapsulation does not work with already fragmented packets.