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 complete working 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 specifically designed for communication network development and analysis and provides extensive details not available in simpler resource-based simulation packages.
• The network hardware and software models are hierarchically structured, which allows a wide 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 layouts using a consistent set of modem user interface methods, such as mouse-controlled menus and icons.
•Automatic simulation generation – OPNE! reduces the effort required to develop a simulation by providing an efficient event-driven 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 thus drastically reduced.
• Analysis Tool – Design debugging, evaluation, and tradeoff analysis require the engineer to interpret large volumes of simulation results. A set of analysis tools and an interactive debugger provide sophisticated data reduction techniques to summarize simulation results in an easy-to-interpret 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, 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.
The specification of processes in C is facilitated by an extensive library of support procedures that provide a wide range of simulation services. Additionally, code specified externally to the OPNET system can be linked to simulations produced by OPNET. This ability to integrate completely general high-level language code gives the user a very high degree of flexibility in building models at any level of detail.
OPNET can be used in many diverse application areas of communication networks. Some examples of possible applications include local area networks, mobile packet radio networks, ISDN architecture, distributed sensors and control networks and tactical networks.
Modeling domains
The OPNET simulations are based on four separate modeling domains called Network, Node, Process, and Link. Illustrates, network models are based on the definition of node models that in turn incorporate process models. In addition, link models are used to characterize links in the network domain. The design methodology for simulation is usually bottom-up, as the user first creates process models, then builds node models that incorporate the processes, and finally builds network models that are completed with node models.
Communicate 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. The process models use a library of kernel procedures that support packet access, network variables, statistics collection, packet communication, and other simulation services.
The binding domain enables 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 that provides flexibility to specify the transmission media 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 run specified process models as finite state machines. The generator module stochastically produces packets according to the user-specified probability density function. The transmitter and receiver modules are the interface for the link-level modules that transfer packets between nodes.
On the network, domain node models are instantiated, and each instance can be assigned separate attributes including identification 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 linked physical 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 layout; These are the network editor, node editor, process editor, parameter editor, and probe editor. The simulation area consists of the simulation tool and the simulation core. The analysis area consists of the Analysis Tool, which processes and graphically presents the simulation results, and the Filter Editor, which is used to build specialized result processing filters. These three areas are graphically supported by an encompassing window management system called Tool
Network editor:
The tool is used to specify network models, consisting of node and subnet objects. Node objects are the physical instantiation of node models built in the Node Editor, while the subnet, as well as the top or global modeling level, nodes can be placed on a dimension plane for those models where the physical location is relevant. Since 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. The types of modules supported include general processors, generators, queues, transmitters and receivers, and antennas.
Process editor:
This tool is to specify process models that represent tools, algorithms or, in general, decision-making processes. The specifications are based on finite state machine representations in proto-c language and include the names of states, transitions between states, the conditions for each transition, the actions that are taken when entering or exiting a state or when making the transition. , temporary and state variables, and formal attributes of the process.
Parameter editor:
This tool includes several different edit modes that are used to specify model parameters that are more complex than simple string or numeric input. Parameter types include functions of one or two independent variables, which are specified graphically, and data tables, which are specified using a spreadsheet-like interface. The parameters created in the editor are: probability density function (PDF), packet formats, interface information formats (ICl) and also for OPNET / B, antenna patterns and modulation function.
Probe editor:
This tool is used to specify data collection requests that can be applied to a run-time simulation 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 of which refers hierarchically to a statistic, a module, a node, and a subnet.
Simulation tool:
The simulation tool provides an environment for configuring one or more simulation runs, specifying their input parameters, and directing their 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 data resulting from the simulation that has been requested by probes defined in the Probe Editor or collected through global statistical reporting mechanisms. Data vectors can be plotted with a variety of chart types. Scale values obtained from multiple simulation runs can be collected and plotted to perform sensitivity analysis for the user-defined independent model parameter.
