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Basic Tutorial: Hello World Example

1. Developing a Script for an Experiment

As explained in the previous overview page, to run an experiment on the testbed a user needs to first describes this experiment in a script. This script is then passed on to a Node Handler, which will use it to run and control the experiment execution. This process is illustrated on the following fig 1.

This script contains the experiment configuration and scenario. More precisely, it includes:

• a description of the required resources (e.g. nodes on the testbed, applications to run),
• their initializations and optional associations (e.g. nodeX is connected to NodeY, all nodes use channel 6 of 802.11g),
• a description of their operation throughout the experiment duration (e.g. applicationX starts at T0 and run for 60sec, nodeY switch wireless configuration after 100sec).

ORBIT experiment scripts are written using the Ruby scripting language. However, a user does not necessary need to be familiar with Ruby to be able to write and run simple experiments. The only prerequisite skills are some prior basic knowledge and practice of any other scripting and/or programming languages (e.g. python, perl, c, java,…). Of course, to be able to develop more complex experiment, a user will have to learn basics of Ruby and read about ORBIT-specific Ruby methods at some stage (more on these two issues at the end of this tutorial).

Figure 1. Execution of an Experiment from a User's point-of-view

2. "Hello World" experiment

In this basic experiment, we define two groups of node: a sender and a receiver group. Although a group of node can contain several nodes, in this simple case each group contains only one node. We also associate a traffic generator application to the sender group, and a traffic sink application to the receiver group. We then define the configuration of the wireless interfaces on the nodes within these groups. Finally, we describe the successive actions to execute in order to perform the experiment.

The script for this experiment is shown below.

#
# A)  Define the 'sender' group, which has the unique node [1,1]
#     Nodes in this group will execute the application 'test:proto:sender'
#
defGroup('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"
}

#
# B)  Define the 'receiver' group, which has the unique node [1,2]
#     Nodes in this group will execute the application 'test:proto:receiver'
#
defGroup('receiver', [1,2]) {|node|

  node.prototype("test:proto:receiver" , {
    'protocol' => 'udp'
  })

  node.net.w0.mode = "master"
}

# 
# C)  Configure the wireless interfaces of All the Nodes involved in 
#     this experiment
#
allGroups.net.w0 { |w|
  w.type = 'b'
  w.channel = "6"
  w.essid = "helloworld"
  w.ip = "%192.168.%x.%y"
}

#
# D)  When all the nodes are turned On and the all the applications
#     are installed and ready, we can start to perform the experiment
#
whenAllInstalled() {|node|

  wait 30 

  allGroups.startApplications
  wait 40

  Experiment.done
}

3. Understanding the "Hello World" script

As you noticed the "Hello World" script is almost human-readable, and is quite understandable to any computer-literate reader. As already mentioned above, deep Ruby knowledge is not a prerequisite to running experiment on the ORBIT testbed.

• The first part of this script uses the ORBIT method defGroup to define a group of nodes called sender, which contains a unique node [1,1]. Next, we perform some specific configurations on the node(s) within the group sender. These specific configurations are described in a block (e.g. curly braces) that directly follows the defGroup call. Within this block, we first assign a particular application to the sender node(s). This application is a traffic generator and is accessed via a prototype which is called test:proto:sender in this example. A prototype can be viewed as a wrapper around an existing application. It defines some set of properties (i.e. "parameters"), which allows us to customize the wrapped application for the specific need of an experiment. For example in this case, through the prototype we can set the address of the sender, and various parameters of the traffic generator itself, such as packet size, rate, and the protocol over which to send the traffic. Prototypes are normally defined in separate files, and the ORBIT platform has a set of predefined prototypes for some basic applications. For example, the prototype "test:proto:sender" is a wrapper around the application "otg" (orbit traffic generator). Other tutorials (see main page) describes how to write your own prototypes for your own or existing applications. The last line on this 'sender' block configures the first wireless interface w0 on the node(s) in this block into managed mode.

#
# A)  Define the 'sender' group, which has the unique node [1,1]
#
defGroup('sender', [1,1]) {|node|        
           
  # Assign the prototype "test:proto:sender" to the node(s) in this group
  node.prototype("test:proto:sender", {

    # Configure the properties for this prototype, i.e. the parameters for the wrapped application
    'destinationHost' => '192.168.1.2',
    'packetSize' => 1024,
    'rate' => 300,
    'protocol' => 'udp'
  })

  # Configure the wireless interface "w0" of the node(s) in this group
  # Put the interface into "Managed" mode. 
  node.net.w0.mode = "managed"
}

• The second part of the script is very similar to the previous one. Here we define a 'receiver' group with a unique node, this time node [1,2]. Again we define some specific configuration for the 'receiver' nodes in a block following the defGroup call. In this case, we assign a traffic sink application to the node(s) via a prototype called "test:proto:receiver", we also set the 'protocol' property of this prototype. Finally, we configure the "w0" wireless interface of the node(s) into "master" mode.

#
# B)  Define the 'receiver' group, which has the unique node [1,2]
#
defGroup('receiver', [1,2]) {|node|

  # Assign the prototype "test:proto:receiver" to the node(s) in this group
  node.prototype("test:proto:receiver" , {
    'protocol' => 'udp'
  })

  # Configure the wireless interface "w0" of the node(s) in this group
  node.net.w0.mode = "master"
}

• The third part of the script presents an example on how to configure interfaces on all nodes in one place to ensure consistency. The command allGroups.net.w0 describes the first wireless interface on all nodes in the experiment. The code inside the following block (e.g. curly braces) configures various parameters of these interfaces. In this specific example, we configure the interface as an 802.11b type, set the essid to a common string, and set it's IP address. We obviously do not want to set all the interfaces to the same IP address, thus any string beginning with a '%' is personalized for each node by replacing characters prefixed by a '%' with a local string. In this specific example, '%y' is replaced by the 'y' coordinate of the node. For this specific experiment setup, the IP address of node [1,1] will be 192.168.1.1, while node [1,2] will have 192.168.1.2 assigned. This part concludes the configuration phase of the experiment.

# 
# C)  Configure the wireless interfaces of All the Nodes in this experiment
#
allGroups.net.w0 { |w|
  w.type = 'b'
  w.channel = "6"
  w.essid = "helloworld"
  w.ip = "%192.168.%x.%y"
}

• This final part of the script describes the operation to execute in order to perform the experiment. An ORBIT experiment script basically defines a state machine, or more precisely, what sequence of commands should be executed if the experiments enters a particular state. The only state we will use in this experiment is whenAllInstalled. This state is reached when all the nodes are configured and all the requested applications are installed and ready to go. The sequence of commands to perform are given in a block following the whenAllInstalled call. The first command 'wait 30' will suspend the execution for 30 seconds to ensure that indeed everything has settled. The allGroups.startApplications will then send a command to all nodes to start the applications assigned to them (via the use of prototypes) in the previous script parts. Thus in this example, this command will start a traffic generator on node [1,1] and a corresponding sink on node [1,2]. The different parameters for these applications are taken from the above definition as well. Finally, the next line 'wait 40' will suspend the control of the experiment for 40 seconds (during which the applications on the nodes will run and exchange traffic), before concluding the experiment with a call to Experiment.done.

#
# D)  When all the nodes are turned On and the all the applications
#     are installed and ready, we can start to perform the experiment
#
whenAllInstalled() {|node|
  
  # Wait 30sec
  wait 30 

  # Start all the Applications on all the nodes
  allGroups.startApplications

  # Wait for 40sec
  wait 40

  # Stop the experiment execution
  Experiment.done
}

• You can find detailed description of all the various experiment-specific scripting commands (such as defGroup, allGroups, whenAllInstalled, etc…) in the Node Handler document page here

4. Running the "Hello World" experiment

Before being able to run this experiment, you should:

• ​Register for an account (if you have not done so yet)
• ​Make a reservation on the Scheduler for a time slot on one of the sandbox testbed
• Log into the console machine corresponding to this testbed. To control the Node Handler, your experiment, and the nodes on the testbed(s), you will use the generic orbit command and its options.

   # User Bob reserved a time slot on the sandbox1 testbed. 
   # He then can access the sandbox1 console using the command:
  
   ssh bob@console.sb1.orbit-lab.org
  
   # To see a list of commands available through the orbit command:
   orbit help
  
   # which will give the following output
   Run a command on the testbed(s)
  
   Usage: orbit [COMMAND] [ARGUMENT]...
  
   Available COMMANDs:
  
     help   Print this help message or a specif command usage
     exec   Execute an experiment script
     load   Load a disk image on a given set of nodes
     save   Save a disk image from a given node into a file
     tell   Switch a given set of nodes ON/OFF
     stat   Returns the status of a given set of nodes
  
   To get more help on individual commands: 'omf help [COMMAND]'
   Examples:
             orbit help exec   Return usage/help for the 'exec' command
             orbit help load   Return usage/help for the 'load' command
  
  

• Install a disk image which includes nodeAgent4 on the nodes of this testbed. For example, you can use the latest baseline.ndz disk image. This disk image installation is done using the orbit load command above. Detailed instructions on how to perform such disk image installation on the nodes on a testbed can be found here.

Once the nodes have been imaged, you can run the "Hello World" experiment with the orbit exec command as follows:

orbit exec --tutorial

Normally an experiment is described in a script file, e.g. "my_experiment.rb", which is run by using the command "orbit exec my_experiment". However in this particular case, the tutorial script is already stored in a repository known by the orbit exec application. Thus the "—tutorial" option instructs the orbit exec application to fetch that script and execute it.

After running the above command, your console output should look like this:

console.sb1:~# orbit exec --tutorial
DEBUG Experiment: Domain: sb1
 INFO init: NodeHandler Version 4.2.0 (1272)
 INFO init: Experiment ID: sb1_2007_11_19_19_15_19
 INFO Experiment: load system:exp:stdlib
 INFO prop.resetDelay: resetDelay = 210:Fixnum
 INFO prop.resetTries: resetTries = 1:Fixnum
 INFO Experiment: load test:exp:tutorial-1a
 INFO stdlib: Waiting for nodes (Up/Down/Total): 0/2/2 - (still down: n_1_2,n_1_1)
 INFO stdlib: Waiting for nodes (Up/Down/Total): 0/2/2 - (still down: n_1_2,n_1_1)
 INFO stdlib: Waiting for nodes (Up/Down/Total): 0/2/2 - (still down: n_1_2,n_1_1)
 INFO stdlib: Waiting for nodes (Up/Down/Total): 0/2/2 - (still down: n_1_2,n_1_1)
 INFO stdlib: Waiting for nodes (Up/Down/Total): 0/2/2 - (still down: n_1_2,n_1_1)
 INFO stdlib: Waiting for nodes (Up/Down/Total): 0/2/2 - (still down: n_1_2,n_1_1)
 INFO n_1_1: Device 'net/w0' reported Not-Associated
 INFO stdlib: Waiting for nodes (Up/Down/Total): 1/1/2 - (still down: n_1_2)
 INFO whenAll: *: 'apps/app/status[@value='INSTALLED.OK']' fires
 INFO n_1_1: Device 'net/w0' reported 00:60:B3:25:BF:F5
 INFO n_1_2: Device 'net/w0' reported 00:60:B3:25:BF:F5
 INFO OML: Started: {"port"=>"7600", "iface"=>"eth2", "addr"=>"224.0.0.6"}
 INFO Experiment: DONE!
 INFO ExecApp: Application 'commServer' finished
 INFO run: Experiment sb1_2007_11_19_19_15_19 finished after 3:41
console.sb1:~#                                          

Congratulation you just ran your first experiment script on the Orbit Testbed!

You will find information on how to collect and interpret measurements and results from your experiment in the next parts of this basic tutorial, here and here

5. Beyond the Basics

5.1. More on the Ruby Language and the ORBIT-specific Ruby methods

As mentioned previously, ORBIT experiment scripts are written in Ruby, an easily understood, extensible, dynamic, object-oriented scripting language. Ruby has been extended into the testbed user's domain with a number of methods. Besides its extensibility and object-orientation, Ruby is concise and consistent. An ORBIT script therefore is written in Ruby primarily using ORBIT-specific methods. Users are encouraged to take look at following resources:

• Ruby Resources
• ORBIT Specific Ruby Methods

5.2. More Tutorials

Once you are done with the remaining parts of this basic tutorial (i.e. collecting and interpreting experiment measurements and results), you might want to have a look at the other tutorials on the main page to further learn about the other ORBIT functions that can help you develop your own complex experiments.

5.3. Definitions of the Prototypes and Application used in the "Hello World" script

• Orbit Traffic Generator (OTG)
  sender.rb is the file that contains the "test:proto:sender" prototype, which wraps around the otg.rb application.
• Orbit Traffic Receiver (OTR)
  receiver.rb is the file that contains the "test:proto:receiver" prototype, which wraps around the otr.rb application.