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Transcript of OPNET IT Guru
IT Guru
Getting Started with IT Guru Academic Edition
Installation
OPNET IT Guru Academic Edition is available for free from OPNET. You may follow their
procedures for applying and installing IT Guru. However, as I have a copy (and registered a
license on behalf of SIIT) it may be easier to follow these steps:
1. Download OPNET IT Guru Academic Edition Build 1998 from ICT Server or the
OPNET official server
2. Install IT Guru.
3. Follow the license activation instructions. You can use my username/password (if you
don't already know it, ask me).
4. Now OPNET IT Guru Academic Edition should be running successfully. You can copy
any files that I have provided into your IT Guru directory at C:\Documents and
Settings\username\op_models\.
From here on, I will refer to OPNET IT Guru Academic Edition as simple IT Guru.
Getting Started
Once you have started IT Guru you can open a project from the File->Open... menu. For this
demo, I will use the project ITS413_WLAN_Simple. The Project window showing two nodes will
be displayed.
The Project window is the main area where you create the network, configure and run the
simulation and view the results. Currently there are two nodes in the demo network: node_0 and
node_1. They look like computers, and as we will see shortly they are models of computers with
wireless LAN interfaces.
To create a network topology you place objects, which are typically nodes (computers, routers,
switches, servers, ...) or links (e.g. Ethernet or optical cable), in the main window. You can select
objects from the Object Palette. Go to Topology->Open Object Palette to bring up the
palette.
For this demo there is no need to add any new objects. But you may practice, and then delete the
objects. Then close the Object Palette.
Once the network topology is created you should configure the nodes and links by editing their
attributes. For the demo we have two nodes. Right click on node_0 and select Edit Attributes.
A list of attributes for that node are shown, along with the values of each attribute. The attributes
can expand/collapse (click on the + plus sign). The first two attributes are common to all objects:
name and model. The remaining attributes are dependant on the model. Note that node_0 uses
the model wlan_station_adv. This means node_0 represents an wireless LAN station (advanced
model). You can change the attributes by clicking on the value.
Editing Attributes
Lets take a closer look at the Traffic Generation Parameters.
We can specify the characteristics of traffic that this node generates. The parameters are:
Start Time: the time at which the application that generates traffic starts. The value
uniform(0.1,1.0) means the start time will be chosen randomly from the range 0.1 to 1.0.
For example, in one simulation this application might start at time 0.34seconds. In
another simulation it might start at time 0.94seconds.
ON State Time: the application generates traffic when it is ON, and stops sending traffic
when it is OFF. The application alternates between the ON and OFF state. For this demo,
I have set the application be ON for 100000 seconds, then OFF for 0 seconds. That is, it
is always ON.
OFF State Time: see above.
Packet Generation Arguments: when the application is ON, the following attributes
specify the type of traffic generated.
o Interarrival Time: the time between each packet. The application generates
(sends) a packet, waits for the interarrival time, then generates the next packet,
waits for the interarrival time, and so on. The value exponential(0.008) means the
interarrival time is chosen randomly from an exponential distribution with an
average value of 0.008 seconds. In other words, on average 125 packets will be
generated every second.
o Packet Size: the size of each packet. In this demo, the exponential distribution is
used again. The average packet size is 1000 bytes, but of course the actual packet
size may be small (13 bytes), and with much less change, large (e.g. 6000 bytes).
o Segmentation Size: after each packet is generated, the application performs
segmentation, with the maximum packet size of 1500 bytes. Therefore if a 2000
byte packet was generated, the application actually breaks it into two packets
(1500 and 500 bytes).
Stop Time: the time at which the application stops. I have set the application to run
forever (as long as the simulation runs).
The above parameters can be used to model a simple application that sends packets (no
responses). On average node_0 will generate 1Mb/s. Lets say you wanted to change the
interarrival time so that node_0 generated traffic at a rate of 0.5Mb/s. Select the interarrival value
and a window will pop up.
You can change the mean outcome (says to 0.004 seconds), as well as the distribution. If you do
make a change, then before you continue, revert back to the original values for the remainder of
the demo (exponential(0.008)).
Now lets look at the WLAN parameters.
Some of the parameters you will recognise from their names. You can click on the question mark
(?) next to the parameter to see a description. The ones of interest to us at the moment are: Data
Rate (11Mb/s); Rts Threshold (None, meaning RTS/CTS is not used); Buffer Size
(approximately 1Mb).
For our demo, you don't need to make any changes (the values I have chosen are sufficient). You
can take a look at node_1 attributes - they should be identical to node_0. Now we need to choose
the statistics that we want to collect and run the simulation.
Choosing Statistics
When we run the simulation IT Guru will simulate the applications generating traffic and
subsequent communications between the two nodes. We are interested in measuring the
performance of the applications, nodes and entire network. To do so, we must specify statistics
that we want IT Guru to collect when the simulation runs. There are two main types of statistics
that we are interested in.
1. Node Statistics: each node has a set of statistics that can be collected. For example,
node_0 (a wireless LAN station) has statistics about the wireless LAN performance for
this node: data sent, data received, queue size, delay, ... . node_1 has the same set of
statistics. The Node Statistics are reported for an individual node. For example, we may
see the data sent by node_0 is 1,034,549 bits per sceond and for node_1 1,109,732 bits
per second. To select Node Statistics, right click on the node and select Choose
Individual Statistics. The window shown for node_0 is displayed.
2. Global (or Network) Statistics: often we are interested in an overall picture of the
network performance. Global Statistics are collected for all nodes/links in the network.
For example, the total application traffic sent in the network may be 2,014,114 bits per
second. This tells us about the performance of the network, not the performance of
individual nodes. To select Global Statistics, choose Simulation->Choose Individual
Statistcs... and select Global Statistics in the window.
Now that the statistics are chosen, we are ready to run a simulation.
Running a Simulation
To configure a simulation select Simulation->Configure Discrete Event Simulation....
The default options are usually sufficient except you may need to change the duration and the
seed for some scenarios. The duration is the simulation time: for example you want to simulate
two wireless LAN nodes sending packets to each other for 5 minutes. In real-time it may only
take several seconds. The seed is the random seed used in the simulation. If you change the seed
a different sequence of events may occur. For example, if you repeat the simulation of one
scenario using the same seed, the results should be exactly the same. But if you change the seed,
the results will most likely be (slightly) different, even with the same scenario.
The Academic Edition has a limitation on the number of events it can simulation (50 million). If
you run a simulation and a warning is produced indicating the total events exceeded the limit for
Academic Edition, then you may try with a shorted simulation duration (e.g. 4 minutes instead of
5 minutes).
To start the simulation, press the Run button. IT Guru will simulate the network, showing you the
progress (number of events per second it is calculating).
Once the simulation is complete a summary of the messages will be listed, after which you can
Close the window.
Viewing the Statistics
Now that the simulation is complete you can view the results (statistics) by selecting Results-
>View Results from the menu.
You can select the statistics that you want to display on the left, and see a preview on the right.
Press the Show button to see the actual plot of results.
By default, all statistics are shown against time. For example, if the simulation runs for 5 minutes
(300 seconds), the Traffic Sent statistic shows the measured traffic sent (in bits per second) at
each time point (the time points are part of the simulation configuration). Be careful when you
interpret what the plots mean. Often there will be some start-up phase, after which the results
will reach a steady-state. Make sure you can identify the two. Also, note that the statistics are
absolute values versus time. Often you only want to know the average for the entire simulation.
In most cases you can estimate the average from the plot. However for more accurate results, you
may try displaying an average (instead of absolute) value. You can do so by selecting the display
type in the preview window on the right. Select As Is, and change it to average or another type,
select Show and observe the difference.
After you show the results, when you close them you are given the option to either Delete or
Hide. If you hide the window, then you can view it again be selecting from the menu: Results-
>Panels or Results->Arrange Panels->Show All.
Scenarios
Within a single project you may have muliple scenarios. For example, you may have one
network topology (scenario) with 2 nodes and then another with 5 nodes. You can create new
scenarios, duplicate existing ones and switch between scenarios via the Scenarios menu.
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