WIRELESS COMMUNICATION:MOBILE IP
Wireless communication is the transfer of information over a distance without the use of electrical conductors or "wires". In this paper we discuss how Mobile IP works and the advantages of it in wireless communication.
In IP networks, routing is based on stationary IP addresses, similar to how a postal letter is delivered to the fixed address on the envelope. A device on a network is reachable through normal IP routing by the IP address it is assigned on the network.
The problem occurs when a device roams away from its home network and is no longer reachable using normal IP routing. This results in the active sessions of the device being terminated. Mobile IP was created to enable users to keep the same IP address while traveling to a different network (which may even be on a different wireless operator), thus ensuring that a roaming individual could continue
communication without sessions or connections being dropped.
Because the mobility functions of Mobile IP are performed at the network layer rather than the Physical layer, the mobile device can span different types of wireless and wire line networks while maintaining connections and ongoing applications. Remote login, remote printing, and file transfers are some examples of applications where it is undesirable to interrupt communications while an individual roams across network boundaries. Also, certain network services, such as software licenses and access privileges, are based on IP addresses. Changing these IP addresses could compromise the network services.
The Mobile Internet Protocol, or better known as Mobile IP, is a protocol that adds to the already
Existing Internet Protocol by making the movement of a node transparent to applications on its original Network. One knows that a host address is made up of a network number and a host part. This network Number tells the user what network the host is attached to. Original Internet Protocol algorithms tell certain Routers how to get packets to their correct networks. Now with the regular Internet Protocol if the host
Disconnected itself from its original network and joined another network, the host would never receive any Packets because the host has the same IP address from its old network that would not be recognized by the
Network in which it joined. In essence the host would seem to be missing because its IP address does not match its new network number and therefore would never receive any packets.
Because of this problem, Mobile IP was created so that mobile nodes could freely move from Network to network without the fear of losing data or interrupting current computer applications and Settings.
2. Components of a Mobile IP Network
Mobile IP has the following three components, as shown in Figure:
• Mobile Node
• Home Agent
• Foreign Agent
A node (a host or router) can change its connection with the Internet by hopping from link (a Medium that allows communication at the link-layer of the OSI-model) to link, while the session is maintained with a permanent IP-address.
A router with an interface on the Mobile Node's home network (Home Link). The Home Agent ensures that:
• A list is maintained of the Mobile Node's current location on the Internet also called its care-of address;
• the traffic that has the Mobile Node as its destination is intercepted. To this end the Home Agent advertises itself on the home network with the Mobile Node's address, drawing all traffic addressed to the Mobile Node;
• All intercepted traffic is tunneled to the Mobile Node's current location.
The foreign agent is a router on the network that is visited (Foreign Link) by the Mobile Node.
The Foreign Agent:
• tells the Home Agent where the Mobile Node resides;
• in some cases functions as the end node of the tunnel;
• in some cases provides a care-of address for the Mobile Node;
• functions as a default router for the Mobile Nodes that have registered with it.
3. How Mobile IP Works
This section explains how Mobile IP works. The Mobile IP process has three main phases, which are discussed in the following sections.
• Agent Discovery
During the agent discovery phase, the Home Agent and Foreign Agent advertise their services on the network by using the ICMP Router Discovery Protocol (IRDP). The Mobile Node listens to these advertisements to determine if it is connected to its home network or foreign network.
The IRDP advertisements carry Mobile IP extensions that specify whether an agent is a Home Agent,
Foreign Agent, or both; its care-of address; the types of services it will provide such as reverse tunneling
and generic routing encapsulation (GRE); and the allowed registration lifetime or roaming period for
Visiting Mobile Nodes. Rather than waiting for agent advertisements, a Mobile Node can send out an agent
Solicitation. This solicitation forces any agents on the link to immediately send an agent advertisement.
If a Mobile Node determines that it is connected to a foreign network, it acquires a care-of address. Two types of care-of addresses exist:
• Care-of address acquired from a Foreign Agent
• Colocated care-of address
A Foreign Agent care-of address is an IP address of a Foreign Agent that has an interface on the foreign network being visited by a Mobile Node. A Mobile Node that acquires this type of care-of address
can share the address with other Mobile Nodes. A colocated care-of address is an IP address temporarily assigned to the interfaceof the Mobile Node itself. A colocated care-of address represents the current position of the Mobile Node on the foreign network and can be used by only one Mobile Node at a time.
When the Mobile Node hears a Foreign Agent advertisement and detects that it has moved outside of its home network, it begins registration.
The Mobile Node is configured with the IP address and mobility security association (which includes the shared key) of its Home Agent. In addition, the Mobile Node is configured with either its home IP address, or another user identifier, such as a Network access identifier.
The Mobile Node uses this information along with the information that it learns from the Foreign Agent advertisements to form a Mobile IP registration request. It adds the registration request to its pending
list and sends the registration request to its Home Agent either through the Foreign Agent or directly if it is using a colocated care-of address and is not required to register through the Foreign Agent. If the registration request is sent through the Foreign Agent, the Foreign Agent checks the validity of the registration request, which includes checking that the requested lifetime does not exceed its limitations, the requested tunnel encapsulation is available, and that reverse tunnel is supported. If the registration request is valid, the Foreign Agent adds the visiting Mobile Node to its pending list before relaying the request to the Home Agent. If the registration request is not valid, the Foreign Agent sends a registration reply with appropriate error code to the Mobile Node.
The Home Agent checks the validity of the registration request, which includes authentication of the Mobile Node. If the registration request is valid, the Home Agent creates a mobility binding (an association of the Mobile Node with its care-of address), a tunnel to the care-of address, and a routing entry for forwarding packets to the home address through the tunnel. The Home Agent then sends a registration reply to the Mobile Node through the Foreign Agent (if the registration request was received via the Foreign Agent) or directly to the Mobile Node. If the registration request is not valid, the Home Agent rejects the request by sending a registration reply with an appropriate error code.
The Foreign Agent checks the validity of the registration reply, including ensuring that an associated registration request exists in its pending list. If the registration reply is valid, the Foreign Agent adds the Mobile Node to