Roaming communication model - Mobile Communication

Roaming Communication Model Ė Mobile Telephony

Now let us discuss a totally different situation involving communication between P1 and P2.

But in this scenario instead of using the conventional landline telephone, now they communicate using cell phones. Let say the telephone number of P2 is 9999999999.

In the beginning both are staying in delhi, and P1 wants to communicate with P2.

So as per the prerequisites P1 knows P2ís cell phone number and P1 can communicate with P2.

Figure- Figure.

But now in this case P1 continues to stay in Delhi while P2 continues to move outside Delhi.

Now in this case, if P1 had to speak to P2, he has to know the fully qualified address of P2, but how can he compute the fully qualified address of P2, P2 is on a move and its location is continuously changing. Since the location of P2 is not constant, P1 will never be able to compute the fully qualified address and hence P1 cannot speak with P2.

Figure- Figure.

So the first part of the problem is .. how do we get the fully qualified address of an object which is on continuous move or is continuously changing its location

I hope we realize we are discussing about the roaming communication model of mobile telephony.

So how is this problem solved?

But I am sure we all know it works , so how does it work ?

Also do we remember while P2 is on move and if P1 makes a call, P1 is never aware that P2 is not in Delhi or P1 continues to believe that P2 is in Delhi while he is not.

Why does P1 continue to believe that P2 is in Delhi while he is not?

This is because while P1 was dialing the number of P2 , he continued to dial it the normal way ie 9999999999 instead of prefixing 0 to the number(in India for any STD call 0 is appended to the original number for a STD call). ie we donít make P1 change the way he interacts with P2.

Now let us think, who is charged for a roaming call?

It is the Roaming Entity (P2) who is charged extra for the roaming call, never ever the caller (P1) will be charged extra for a remote call because if we start charging extra amount from the caller P1 for a roaming call , he will come to know that P2 is not available in the local city.

Also we will realize that P1 is charged for a local call although P2 is not in the same City, thatís because the systems are designed in such a way so that the location of P2 is transparent to P1 ie P1 continues to believe that P2 is in the same address space although , P2 is not.

Such a communication model is called Location Transparency Based Distributed Communication Model because the location of the target object is transparent or not known to the caller.

So there are two problems to be solved

  1. How does a person find out the fully qualified address of an object which is on continuous move?
  2. How is location transparency achieved in the roaming communication model?

Let us try solving the problem of location transparency first .. for us to understand the same , lets quickly look into the following analogy

Hemant Jha
Founder - VPlanSolutions
Researcher, Trainer