Examining The Features Of The OPNET Information Technology Essay

OPNET (Optimized Network Engineering Tools) is a huge software having possibilities to simulate large area networks with various protocols. It was basically developed for military usage but it has grown unexpectedly large to become a leading commercial simulation tool for networks. It is expensive software to buy but its free licenses are available for educational usage.

“It is a network simulation tool that allows the definition of a network topology, the nodes, and the links that go towards making up a network. The processes that may happen in a particular node can be user defined, as can the properties of the transmission links. A simulation can then be executed, and the results analyzed for any network element in the simulated network” [1].

4.2 Features of OPNET:

With this engineering system different communication networks can be simulated with detailed protocol modeling and having options of performance analysis. The features of Opnet includes simulation kernel, object based modeling and graphical specification of models. Different predefined node models are available in Opnet libraries which can be used by simply importing and enabling the desired functions. OPNET has the feature to build different models, to run and execute different simulations and one can set different parameters to see the desired output.

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OPNET is simulation tool that operates at packet level, it can simulate a wireless network as well. In OPNET all the simulations are in a hierarchy, each level of the hierarchy shows what is going on at that particular level of the model that is simulated. It has the feature to debug the simulation if an error has occurred. The major three tools of OPNET are modeling tool, Simulation and Execution tool and Result Analysis tool. Any network can be analyzed and implemented by using these three tools of OPNET.

4.3 The Model Development Tool:

The model development tools consist of the

Network Editor

Node Editor

Process Editor

4.3.1 Network Editor:

Physical topology of a network is created in network editor by defining nodes and links between them. There are three main types of nodes fixed, mobile and satellite. These nodes can be modified as per the usage. Simplex or Duplex links can be used for communication between these nodes. Here at network level links can also be customized to simulate the channels of communication. For broadcasting to multiple devices attached a bus link can be used. One can create a subnet to avoid complexity created by a large number of nodes.

4.3.2 Node Editor:

The Node Editor is used to place the models of the nodes used into the network. A node can contains modules like Processors, Queues, Sink, Point to Point Transmitter and Receiver, Bus transmitter and receiver, Radio transmitter and receiver and external system modules. They can be connected through packet streams and statistic lines [2].

Figure: 4.1 (Node Model)

In this figure different processers are used to create the complete node model, blue links are of packet stream, red links are static wires and orange links are logical Tx/Rx Associations.

4.3.3 Process Editor:

Behavior of process model is specified with process editor. The Process Editor is used to define the processes that run inside the modules of node model. The processes are designed using State Transition Diagrams and the codes are written in Proto-C [2].

Figure: 4.2 (Process Model)

Pointing arrow in the figure shows initial state, the green color of the state indicates that it is forced while red is for unforced state, the arrow headed lines indicate transition between states. Upper half is ‘Enter Executive’ and lower half is ‘Exit Executive’ of state. 33/0 shows the number of lines of code written in ‘Enter/Exit Executive’ of state. The code is shown in the figure below.

Proto C is used to write codes in Enter Executive, Exit Executive and Transition Executives. The code written in Enter Executive is executed when module is entering a state, the code written in Exit Executive is executed when module is leaving a state and in response to an event transition executive code is executed.

4.4 Model design:

In OPNET, models are created in a hierarchy, here network level is at the top followed by node level, which in order is made from the process level. Network editor, Node editor and Process Editors are used to implement network level, node level and process level design respectively. At top there is network level which may or may not contains subnets, further in these subnets there may be more subnets. This is how OPNET represents hierarchical structure of a network.

Packet generation, reception, error checking, forwarding it to other processes is done at node level. State transition diagrams with codes written in Proto-C are used to define processes which can be modified by the user to create a process of own usage at process level.

4.5 Running a simulation:

After defining all the models of the network system, we can run a simulation in order to study system performance and behavior using the simulation execution tools described earlier. To change simulation behavior OPNET provides various options to make changes including internal and external execution, changes can also be made to configure attributes for changing simulation’s behavior. It also supports running of simulation independently from OPNET graphical tool. The services obtained by simulation tool are :

Attribute values and simulation sequence

Simulation sequence’s execution

Capturing simulation sequence in file for later usage

To collect desired output data Probe editor is used, statistical and animated output data can be collected by customizes animation option. Probe editor is used to select different output formats. List of probes is defined by grouping multiple probes by the user and are applied to the model when executed.

4.6 Data observation and collection:

Result analysis tool consists of filter and analysis tool in order to observer and collect data after the simulation execution has been completed. In OPNET different simulations are used to create different outputs, as mentioned above. OPNET debugger provides detailed traces, animation and numerical data of several types to be used in order to create outputs after the execution of a simulation.

Simulations in OPNET supports an open interface to C language, enabling simulation developers to create copy right protected output messages, console windows, ASCII/binary files and live connections for communication with other programs. But, commonly animation data and numerical statistics are most usable forms of output which are directly supported by simulation kernel. To view animation data generated by automatic simulation probes, simulations kernel has a package called Anim package and to view data generated by statistic probe, simulation kernel has a package called Stat package [3].

Analysis tool is used to display data in graphical form. Representation of a graph is in rectangular area called analysis panel. Graphs can be generated by performing various operations to create a new set of data. There are two axis of this analysis panel horizontal axis and vertical axis, these axis creates a plotting area used to plot different stats in the form of graphs as shown in the figure below.

Figure: 4.3 (analysis panel)

Data can be extracted from the simulation output files and can be displayed in different forms. With this tool one can calculate probability density function and cumulative distribution function as well as generation of histograms. For the performance analysis of a network different graphs can be merged as show in the figure above using Overlaid statistics option.

4.7 The Graphical User Interface:

The graphical user interface (GUI) of modeler 14.5 is much improved from the previous versions of OPNET. It is more user friendly and is provided with a number of options. In addition to create a new project user can edit the existing projects as well. Network editor, node editor and process editor enables the user to create multiple nodes as per requirement of project. User can import traffic, user can fail or recover a link and can run the simulation by simply clicking on buttons shown on the toolbar.

In the network model there is a node model, which can be accessed by double clicking on it. Process model can be accessed inside the node model, inside the node model we have the option to create sinks, queues, servers and packet streams. The option of configuration of different routers, servers, work stations and links is also available at this level.

4.8 Conclusion:

OPNET is a large domain for network modeling that is being used world widely. It enables the user to edit available models at any level i.e. network, node or process level. OPNET has different applications in network modeling, because of the availability of real life models like routers, switches and workstations. Due to its user friendly interface user can make their networks more easily, and can learn the software quickly. For learning the software OPNET provides different tutorials along with the simulation results. In OPNET libraries almost all the network elements are available that are being used and implemented today. There is a huge range of predefined protocols available in OPNET libraries, in addition to these protocols user can develop new set of protocols by using Proto-C. Proto-C is gives an open interface to the users to create their own protocols as it has resemblance with C and C++. The results obtained after the execution of simulation are very much similar to those results obtained in real time scenarios. This feature of OPNET makes it capable of using it at professional level.

REFRENCES

[1] http://www.ee.ucl.ac.uk/dcs/commercial/opnet/opnet.html

[2] www.sce.carleton.ca/faculty/wainer/students/DEVSnet/Opnet.doc

[3] OPNET help