In this chapter, the co-simulation capability of OPNET Modeler is introduced. The co-simulation interface allows OPNET Modeler to interact with external systems during simulation. These external systems can be software programs, hardware devices, or simply humans. Co-simulation is often used in situations where some third-party programs need to be used to process or analyze the intermediate simulation results, or some real-world data needs to be collected and fed back to OPNET Modeler during simulation.

Co-simulation with external programs

Introduction

OPNET Modeler provides a mechanism to support live interaction with an external system during simulation. This co-simulation mechanism involves the following concepts:

• External System Definition (ESD) model. The ESD model defines a set of interfaces that allow processmodels in OPNETmodeler to communicate with external programs. These interfaces can be read or written by both OPNET process models and external programs.

• Esys (External System) module. The Esys module is a node domain module that can be placed into a node domain and processed as are other node domain modules, like processor module and queue module. However, the Esys module has extra features: it supports process models with external system communication capability and supports ESD models. The Esys module allows the user's simulation model to talk to external systems.

• Simulator description file. The simulation description file is a plain-text file containing statements that specify how to build co-simulation. This text file should be placed in the OPNET model directory and has the filename extension “.sd”.

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