Cooja Sensor Network Simulator

Cooja is a simuator that comes with the Contiki operating system. It is very useful for testing sensor network applications written for Contiki platform without having to put them in real sensor network hardware. If we use real hardware motes for testing our Contiki programs, we will have to burn the flash memory of the motes sevaral times until we get a nicely tested program without any known bug. But is not easy to program motes which is a time consuming task. Even if we are ready for that, it may be not good for a mote to reburn its flash memory so many times since the number of read write cycles possible in flash memory is limited.

    Because of these reasons whenever we write a Contiki program, we better try it running on the Cooja simulator first and later on we can go for real hardware. Cooja is written in Java language and has a very modular structure which enables it to be extended with custom made plugins for it. When we compile a Contiki program for running on Cooja, it actually gets compiled into an executable of the native platform which is the operating system where our Cooja simulator is running on. Cooja runs these executables using Java Native Interface(JNI) from a higher level.

    Before using Cooja simulator for testing our programs we have to setup the Environment for it to work properly. First of all download the Contiki source code from here. Let's say you have downloaded it. Inside the contiki source code you can find the Cooja simulators source code in the path /contiki-2.4/tools/cooja. Go through the following steps to prepare the environment. You may skip some steps if your platform already have such configurations. Here I assume you are using Ubuntu Linux as your operating system since it is where I have tested all these stuff.

1) Installing Java
    Since Cooja is written in java, you have to have java installed in your platform. Do the following to install Java. If you have already installed Java, you can skip this step. Open a terminal and issue the following command with an active internet connection.

    sudo apt-get install java-6-openjdk

2) Installing Apache ant
    We use ant as the build tool to compile and build the Cooja simulator from its source. Therefore to install it, issue the following command in a termianl.

    sudo apt-get install ant

3) Setting JAVA_HOME and PATH variables
    Cooja simulator requires the environmental variables JAVA_HOME and PATH to work properly. Therefore follow this link to set those variables.

Now you have the proper environment for running Cooja simuator. It's time to deal directly with Cooja. Open a terminal and goto the downloaded Contiki source code. From there, goto Cooja source code directory which should be in the path /contiki-2.4/tools/cooja. From there issue the following commands.

    ant jar
    ant run

Figure-1

    If everything went fine, you'll get a window like the one showed in the figure-1. It contains only a menu bar. You can test whether all the environment setup has done correctly by using a simple testing wizard provided by Cooja. Open this testing wizard by going through this way.

 menubar >> Settings >> Compiler configuration wizard

Figure-2

You will see the wizard showed in the figure-2 now. Click on the "Start tests" button to begin the test. The first test will be "Compile and link Contiki library" as showed in fugure-3 and click on "Run test" button. If it prints "Test OK", you have done with first test. Click on "Close" button and then "Next test" button. In this way you should go through all the four tests. The final test window will be like the one showed in figure-4. After passing though the final test, you can "Close Wizard".

Figure-3

Figure-4

If one of these test is failed, that means you have missed something when setting up the environment as mentioned above. After passing the tests you can start using Cooja simulator for testing your Contiki programs.

To run the hello-world example which resides inside the examples directory of Contiki source code, do the following steps. Goto "File" menu and clieck on "New simulation" menu item. It will bring a window to create a new simulation. Enter a name for the simulation and click "Create". Now you'll get something like the figure-5. From there goto the menu "Mote Types" and from it click on "Contiki Mote Type". Now from that window, browse for the hello-world.c file in Contiki examples directory. Then click "Compile". After compilation completed, click on "Create" button.

Figure-5

A new window will ask you to add the number of motes for simulation. For now lets type 1 on the text field and then click "Create and Add". In the simulation visualizer window you can see a mote now like a circle. Now in the Control Panel window, set the Delay value to 1ms and click "Start" button. Now you can see the output of the virtual motes that run your program in the Log listener window. You can stop the simulation by clicking on "Pause" button in the Control Panel window.

Figure-6

    Alternatively you have another easy way to quick start your Contiki program with Cooja. To try it, close the Cooja simulator window first. From the terminal goto the hello-world directory in the examples directory of Contiki. From there type the following on the terminal.

       make TARGET=cooja hello-world

This will start the hello-world program with Cooja simulator. There are so many things to explore in Cooja simulator. With the current understanding find about different things you can do with Cooja simulator.