[wiki:WikiStart Orbit] > [wiki:NodeHandler NodeHandler] > [wiki:NodeHandler/Tutorial Tutorial] > Understanding Hello World Experiment Script

= Understanding the tutorial script =
An experiment name is used to create the corresponding database to store results and to create a unique log for the same
{{{
Experiment.name = "tutorial-1a"
Experiment.project = "orbit:tutorial"
}}}
Create a group of nodes called ‘sender’ and assign node1-1 to it
To the group sender, we assign a role that all nodes belonging to this group will 
play. Here, we instruct nodehandler to assign the prototype sender to node1-1 
Note that the ‘sender’ prototype is defined using a corresponding ‘sender.rb’ file 
and is tied to an actual underlying application that will actual get launched on the 
node (In this case, the application is ‘otg’ (ORBIT Traffic Generator)

These are the command line arguments that will be used by nodehandler when it 
asks the nodeagent to launch the application, for e.g, the following will 
description will cause nodeagent to launch ‘otg –destinationHost 192.168.1.3 --
packetsize 1024  --rate 300 -- protocol udp
{{{
defNodes('sender', [1,1]) {|node|                   
node.image = nil   #Default image on the node to be used for the experiment
node.prototype("test:proto:sender", {
   'destinationHost' => '192.168.1.3',
    'packetSize' => 1024,
    'rate' => 300,
    'protocol' => 'udp'
  })
node.net.w0.mode = "ad-hoc"
}
}}}
Create a group of nodes called ‘receiver’ and assign node1-3 to it
To the group receiver, we assign a role that all nodes belonging to this group will 
play. Here, we instruct nodehandler to assign the prototype receiver to node1-3 
Note that the ‘sender’ prototype is defined using a corresponding ‘receiver.rb’ file 
and is tied to an actual underlying application that will actual get launched on the 
node (In this case, the application is ‘otr’ (ORBIT Traffic Receiver)

These are the command line arguments that will be used by nodehandler when it 
asks the nodeagent to launch the application, for e.g, the following will 
description will cause nodeagent to launch ‘otr -- hostname 192.168.1.3 –- protocol udp
{{{
defNodes('receiver', [1,3]) {|node|
  node.image = nil  
  node.prototype("test:proto:receiver" , {
   'hostname' => '192.168.1.3',
    'protocol' => 'udp'
  })
  node.net.w0.mode = "ad-hoc"
}
}}}
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 co-ordinates of the nodes
{{{
allNodes.net.w0 { |w|
  w.type = 'b'
  w.essid = "helloworld"
  w.ip = "%192.168.%x.%y"
}
}}}
Now, start the application, 
This is a barrier where nodehandler waits to receive an OK message from each of
the nodeagents, 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
}}}