Tutorial 1: Hello World Example

In the "Hello World" experiment, a sender node sends a data stream to a receiver node. The script for this experiment is shown below.

#
# Define nodes used in experiment
#
defNodes('sender', [1,1]) {|node|
  node.prototype("test:proto:sender", {
    'destinationHost' => '192.168.1.2',
    'packetSize' => 1024,
    'rate' => 300,
    'protocol' => 'udp'    
  })
  node.net.w0.mode = "managed"
}

defNodes('receiver', [1,2]) {|node|
  node.prototype("test:proto:receiver" , {
    'protocol' => 'udp'
  })
  node.net.w0.mode = "master"
}

allNodes.net.w0 { |w|
  w.type = 'b'
  w.essid = "helloworld"
  w.ip = "%192.168.%x.%y"
}

#
# Now, start the application
#
whenAllInstalled() {|node|
  wait 30 

  allNodes.startApplications
  wait 40

  Experiment.done
}

Figure 1. Script for "Hello World" Experiment

Understanding the Hello World

The first part of the script creates a group called sender and assigns node1-1 to it. Next, we instruct nodehandler to assign the prototype test:proto:sender to node1-1. A prototype is similar to a function or macro in conventional programming languages and defines in this case a re-usable configuration. The prototypes are normally defined in separate files . In this case, the prototype contains instructions to install a traffic generator, but we will learn about this later. What is important here is that a prototype can define properties which allows us to customize it for the specific experiment. In this experiment, we can set the address of the sender, and various properties of the traffic generator itself, such as packet size, rate, and the protocol over which to send the traffic.

defNodes('sender', [1,1]) {|node|                   
  node.prototype("test:proto:sender", {
    'destinationHost' => '192.168.1.2',
    'packetSize' => 1024,
    'rate' => 300,
    'protocol' => 'udp'
  })
  node.net.w0.mode = "managed"
}

The last line 'node.net.w0.mode' configures the first wireless interface w0 to be used in managed mode.

The next block of code defines the receiver in similar fashion. We are using the receiver prototype here which installs a traffic sink. In addition, we are setting the receiver's first wireless interface to master mode.

defNodes('receiver', [1,2]) {|node|
  node.prototype("test:proto:receiver" , {
    'protocol' => 'udp'
  })
  node.net.w0.mode = "master"
}

Configures the first wireless card on all nodes to 802.11b, essid ‘helloworld’ with ip addresses 192.168.x.y where x.y are the grid co-ordinates of the repsective nodes.

allNodes.net.w0 { |w|
  w.type = 'b'
  w.essid = "helloworld"
  w.ip = "%192.168.%x.%y"
}

Now, we start the application. This is like a barrier implementation where nodehandler waits to receive an OK message from each of the nodeagents, and only proceeds when initial configurations are OK.

whenAllInstalled() {|node|

This command will request nodeagents to launch the application corresponding to the role that the node is playing, e.g sender will launch the application otg and the receiver will launch the application otr with the command line options as specified before

allNodes.startApplications

Conduct experiment for 60 seconds

  wait 60

End of experiment – Shut down all nodes

Experiment.done