#distpatch

Note: The content in this series is extracted from the book, Introduction to Network Simulator NS2. You may have to read chapter 4 of the book for better understanding.

Introduction

In programming, we tell computer what to do using a set of instructions called computer program. We can instruct the computer to carry out an action immediately, or to wait a bit before carrying out the action. The former approach is quite straight forward. In C++, I can use printf(...) to print a message on the screen, and the message would appear immediately. 

The latter had always been mystical to me until I learned it with NS2. How can we stop the computer from printing the message and tell it print later? What kind of statement do I use to stop the computer from printing it right away. How can I make up a schedule to do a set of things at a set of given points in time? As we shall see, NS2 does this using what we call "Event-Driven Simulation". 

So, in what follows, I will unravel this seemingly mysterious things. I will explain how NS2 make up a schedule (e.g., starting an FTP flow at 5 second and stop it at 20 second), and make the simulation run according to the predefine schedule.  

In a nutshell, we need to learn the following topics:

The Concept

Event and Handler

Event Scheduler

An Example of Scheduling-Dispatching Mechanism—Delayed Packet Reception

Types and Dynamic of UID (Unique ID)

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T. Issaraiyakul and E. Hossain, “Introduction to Network Simulator NS2”, Springer 2009. Buy it now from Amazon: