Introduction to Mobile IP Concept

Last time, home computer systems are desktop. We always can't carry desktop computer systems to wherever we go. They can't move easily from one place to another. To access internet, they need an address which is Internet Protocol address (IP address). 

Nowadays, modern computer systems are becoming smaller than old models. They can be any consumer devices which have different size such as laptops, smart phones, PDAs, tablets, etc. We can bring them with us. Their nature is mobile. It should have an extraordinary protocol to define their location which are not fixed. it is "Mobile IP".

Supposedly my home is in Ygn, according to the following figure. I can collect the letters which destination is my home address.

The problem is how I should get letters while I am on the business trip. It means that how to handle the situation while I am away from my hometown. But, it is possible to solve the issue if we can apply "Mail Forwarding".

Before I move out, I could inform my new address to Ygn Post Office. And then, Ygn Post Office would forward my letters to my new address which is Mdy. It would be "Mail Forwarding" untill I get home and inform Ygn Post Office to cancel the service.

In this example, there are two Agents mainly. 

Ygn Post Office (Home Agent) provides sending mail to my ygn home regularly.

When I am at my mdy home, it would have mail forwarding via Mdy Post Office (Foreign Agent).

To start Mail Forwarding,

1. Registration to home agent about mail forwarding 

I would inform Ygn Post Office about my new address to start mail forwarding

2. Home agent would forward letters encapsulated by a new address, to foreign agent

According to the registration of mail forwarding, Ygn Post Office will forward my letters to Mdy Post Office which can send it to my mdy home. 

Actually, home agent applies encapsulation technique via foreign agent. Encapsulation is the real world phenomenon that we can see most of the times. Encapsulation is an isolation, and it can cover difficulties to provide convenience.

I believe we all have seen capsules (pharmacy) and tablets (pharmacy). For example, if I have option to take capsules or tablets to cure my pain, I will select capsules because capsule is a container which can keep bitter medicine powder inside and it's easier to take. It provides convenience by an isolation layer between medicine powder and patient. 

This time, let's see our electronic TV. We don't understand about complex electronic circuits but we can use TV. Why? They apply encapsulation. By placing inside it, they hide complexity and also cover their property, avoid to be seen by others. 

When I get ygn home back, I would inform my ygn post office to deactivate mail forwarding. And then I will get letter as usual as before I move out.

In this scenario, we will find the following concept.

Mobile Node:         I, myself
Home Agent:         Ygn Post Office
Home Address:     Ygn Home Address
Foreign Agent:      Mdy Post Office
Care of Address:  Mdy Home Address
Binding:                  Registration of Mail forwarding with Care of Address

Now, the above example will reflect to the mobile internet protocol addressing. According to the following figure, we will find mobile node, home agent, and foreign agent mainly.

Mobile Node:          Laptop
Home Agent:           Router (London)
Home Address:      London IP Address
Foreign Agent:        Router (Japan)
Care of Address:    Japan IP Address
Binding:                    Binding Home Address with Care of Address

Hopefully you will get and enjoy the idea of Mobile IP. 

Reference: 
mobile ip in wiki
tcp/ip guide

tcp/ip in 14 days