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OPNET Introduction

Optimized Network Engineering Tools (OPNET) is a comprehensive engineering system capable of simulating large communications networks with detailed protocol modeling and performance analysis. OPNET has been designed to provide a comprehensive work environment for the network modeler that takes advantage of the sophisticated graphics of engineering workstations. The tools provided by OPNET from a tightly integrated system with the following main features

•Domain-specific hierarchical models -OPNET is designed specifically for the development and analysis of communications networks and provides extensive details not available in simpler resource-based simulation packages.

•The network hardware and software models are hierarchically structured, which allows extensive reuse of the models developed in different simulations. Graphical specification of models: whenever possible, specifications are entered graphically with specialized editors. These editors provide an efficient means of capturing designs through a consistent set of modem user interface methods, such as mouse-controlled menus and icons.

•Automatic simulation generation – OPEN! reduces the effort required to develop a simulation by providing an efficient event-based simulation kernel, communication building block libraries, and compilers that take the design specification and automatically generate an executable simulation. The lengthy software development process typically associated with simulating complex systems is dramatically reduced.

• Analysis Tool – Design debugging, evaluation, and trade-off analysis require the engineer to interpret large volumes of simulation results. A suite of analysis tools and an interactive debugger provide sophisticated data reduction techniques to summarize simulation results in easily interpretable graphical form and to monitor model behavior in detail.

• Flexibility and detailed modeling – While much of the structure model specification in OPNET is done graphically, the protocol and algorithm models employ a hybrid approach called proto-c, which allows users to embed C language code within a finite state machine. graphically specified.

Process specification in C is facilitated by an extensive library of support procedures that provides a wide range of simulation services. In addition, code specified externally to the OPNET system can be linked to simulations produced by OPNET. This ability to integrate fully general high-level language code gives the user a high degree of flexibility in building models at any level of detail.

OPNET can be used in many different application areas of communication networks. Some examples of possible applications include local area networks, mobile packet radio networks, ISDN architecture, distributed sensor and control networks, and tactical networks.

modeling domains

OPNET simulations are based on four separate modeling domains called Network, Node, Process and Linkillustrates, the network models are based on the definition of node models which in turn incorporate process models. Furthermore, link models are used to characterize the links in the network domain. The design methodology for simulation is usually bottom-up in the sense that the user first creates process models, then builds node models that incorporate the processes, and finally builds network models that are populated with node models.

Communication through links.

Process models are specified in the proto-c language that uses a graphical editor to capture the structure of the process in the form of a finite state machine (FSM). The FSM contains the logic of the process model within its states and transitions. Process models make use of a library of kernel procedures that support packet access, network variables, statistics collection, packet communication, and other simulation services.

The binding domain allows for the incorporation of custom or user-specific binding models within the OPNET simulation. The communication link between each pair of transceivers is modeled as a pipeline, which provides flexibility in specifying the means of transmission between any two nodes. Link models are written directly in C and linked to the simulation.

The node domain consists of a set of modules that can be interconnected from arbitrarily complex node architectures. The queue and processor modules execute specified process models as finite state machines. The generator module produces packets stochastically according to the probability density function specified by the user. The transmitter and receiver modules are the interface to the link layer modules that transfer packets between nodes.

In network domain models nodes are instantiated and each instance can be assigned independent attributes including id and position, and user-defined attributes. Within the top level of the network editor, you can also create subnet objects that provide an additional level of abstraction. There are physical linked nodes, radio nodes, mobile nodes, and satellite nodes in the network domain.

system structure

The OPNET system is a set of tools that can be divided into three functional areas: Specification, Simulation, and Analysis. The specification area consists of the five graphical editors with which users specify their design; these are the network editor, the node editor, the process editor, the parameter editor, and the probe editor. The simulation area consists of the Simulation Tool and the Simulation Kernel. The analysis area consists of the Analysis Tool, which processes and graphically presents simulation results, and the Filter Editor, which is used to build specialized result processing filters. These three areas are graphically supported by a comprehensive window management system called Tool

RedEditor:

The tool is used to specify network models, consisting of subnet and node objects. Node objects are physical instances of node models created in the Node Editor, while subnet nodes, as well as top or global modeling level nodes, can be placed on a dimension plane for those models where the physical location is relevant. Because the Network Editor represents the most complete modeling of OPNET, it also provides the operations necessary to unite all the lower-level specifications into a single executable simulation.

node editor:

This tool is used to specify node models, which consist of parameterized modules interconnected in an arbitrarily complex graph to represent the information flow and structural aspects of a particular class of communications node. Supported module types include general processors, generators, queues, transmitters and receivers, and antennas.

process editor:

This tool is for specifying process models that represent decision-making tools, algorithms, or in general processes. The specifications are based on finite state machine representations from the Proto-C language and include the names of the states, the transitions between states, the conditions for each transition, the actions taken when entering or leaving a state, or doing a transition, temporary and state variables, and formal attributes of the process.

Parameter editor:

This tool includes several different editing modes that are used to specify model parameters that are more complex than simple numeric or string input. Parameter types include functions of one or two independent variables, which are specified graphically, and data tables, which are specified through a spreadsheet-like interface. The parameters created in the editor are: probability density function (PDF), packet formats, interface information formats (ICl) and, in addition, for OPNET/B, antenna patterns and modulation function.

sonar editor:

This tool is used to specify data collection requests that can be applied to a simulation at run time to cause the running model to put specific data into an output file. A file created in the Probe Editor consists of a list of probes, each hierarchically referencing a statistic, a module, a node, and a subnet.

simulation tool:

The simulation tool provides an environment for setting up one or more simulation runs, specifying their input parameters, and directing the collected data to named output files. The simulation tool uses a data table for the specification of simulations and their parameters.

Analysis tool:

This tool is used to analyze the resulting simulation data that has been requested using probes defined in the Probe Editor or collected through global statistics reporting mechanisms. Data vectors can be plotted with a variety of chart types. Scaler values ​​obtained from multiple simulation runs can be collected and plotted to perform sensitivity analysis for the user-defined independent model parameter.