OMNeT++ Overview

Relevant source files

Purpose and Scope

This page provides a high-level introduction to the OMNeT++ discrete event simulation framework. It covers the framework's architecture, major components, and design philosophy. OMNeT++ is primarily used for building network simulations, but its generic component model makes it suitable for queueing networks and other complex discrete event systems.

For detailed information about specific subsystems, see:

Installation and setup: Getting Started and Installation
Learning resources: Sample Simulations and Tutorials
Core simulation mechanics: Core Simulation Framework
NED and MSG domain-specific languages: NED and MSG Languages
Result collection and analysis: Result Analysis and Visualization
Building simulation models: Build System and Environment Setup

Sources: include/omnetpp/simkerneldefs.h25-32 Version1

What is OMNeT++

OMNeT++ is a C++-based discrete event simulation (DES) framework. In a discrete event system, state changes (events) happen at discrete instances in time. Between events, the system state remains constant doc/src/manual/ch-simple-modules.tex26-34

The framework provides:

A simulation kernel (simkernel) for event scheduling, component management, and message delivery doc/src/manual/ch-simple-modules.tex70-72
Domain-specific languages: NED (Network Description) for defining model topology and MSG (Message Definition) for message/packet structures doc/src/manual/ch-ned-lang.tex1-3 doc/src/manual/ch-message-definitions.tex1-3
Execution Environments: Qtenv (Qt-based graphical interface) for debugging/animation and Cmdenv (command-line) for high-performance batch runs doc/src/manual/ch-run-sim.tex1-3
Result Analysis: A combination of C++ recording backends and a Python-based analysis API for processing simulation outputs doc/src/manual/ch-ana-sim.tex1-3
IDE: An Eclipse-based environment with specialized editors for NED, MSG, and INI configuration files ui/ChangeLog30-64

Sources: doc/src/manual/ch-simple-modules.tex26-34 doc/src/manual/ch-ned-lang.tex1-3 doc/src/manual/ch-message-definitions.tex1-3 doc/src/manual/ch-run-sim.tex1-3 doc/src/manual/ch-ana-sim.tex1-3 ui/ChangeLog30-64

Core Architecture

OMNeT++ follows a layered architecture where models are defined through a mix of NED, MSG, and C++ code, which are then compiled into a simulation executable.

Natural Language to Code Entity Space: Architecture Map

Sources: src/nedxml/ChangeLog156-161 src/nedxml/ChangeLog18-22 src/utils/ChangeLog29-31 src/qtenv/ChangeLog194-206 src/cmdenv/ChangeLog1-10

Major Components

Simulation Kernel

The kernel manages the simulation lifecycle and the hierarchy of components. Most library classes derive from cObject for basic services like name storage and metadata doc/src/manual/ch-sim-lib.tex55-59

Class	Purpose
`cSimulation`	The central object that owns the network and the Future Event Set (FES) doc/src/manual/ch-simple-modules.tex70-72
`cModule`	Base class for hierarchical components; simple modules contain C++ logic, compound modules contain submodules doc/src/manual/ch-simple-modules.tex6-11
`cMessage`	Represents events. It is sent between modules and scheduled in the FES doc/src/manual/ch-simple-modules.tex120-125
`SimTime`	A 64-bit integer based decimal fixed-point representation for simulation time doc/src/manual/ch-simple-modules.tex154-156
`cIRngManager`	Pluggable Random Number Generator manager mechanism include/omnetpp/ChangeLog31-34

Sources: doc/src/manual/ch-simple-modules.tex6-11 doc/src/manual/ch-simple-modules.tex70-72 doc/src/manual/ch-simple-modules.tex120-125 doc/src/manual/ch-simple-modules.tex154-156 doc/src/manual/ch-sim-lib.tex55-59 include/omnetpp/ChangeLog31-34

Component Model and NED

OMNeT++ models are hierarchical. The Network Description (NED) language is used to declare:

Modules: Types and their parameters/gates doc/src/manual/ch-ned-lang.tex1-3
Channels: Links between gates (e.g., cDatarateChannel, cDelayChannel) that define delay, loss, and datarate src/nedxml/ChangeLog13-14
Submodules: Instances of other modules inside a compound module.

Natural Language to Code Entity Space: Component Lifecycle

Sources: doc/src/manual/ch-simple-modules.tex76-87 src/sim/ChangeLog176-180 src/sim/ChangeLog182-183 src/qtenv/ChangeLog112-118 src/envir/ChangeLog163-165

User Interfaces

The kernel is decoupled from the UI via the cEnvir interface.

Qtenv: Provides a rich graphical environment for inspecting objects, viewing logs, and visualizing the simulation on a 2D cCanvas or 3D cOsgCanvas. It features a Generic Object Inspector with "Children" and "Details" modes src/qtenv/ChangeLog40-52 include/omnetpp/ChangeLog199-205
Cmdenv: Optimized for batch execution, supporting parallel simulation (parsim) and fingerprint-based regression testing src/cmdenv/ChangeLog1-10 src/utils/ChangeLog5-12

Sources: src/qtenv/ChangeLog1-30 src/envir/ChangeLog91-104 src/cmdenv/ChangeLog1-10 src/utils/ChangeLog5-12

Result Recording and Analysis

Simulation results are collected using a signal-based mechanism.

Signals & Statistics: Modules emit() signals. The @statistic property in NED defines how these signals are recorded into result filters and recorders src/sim/ChangeLog117-124 include/omnetpp/ChangeLog118-120
Storage: Data is written to .vec (vector) and .sca (scalar) files, supporting both text and SQLite formats src/envir/ChangeLog98-104
Analysis: The Scave toolset allows users to process these files. It includes an Eclipse-based editor and a Python API (omnetpp.scave) for high-level data manipulation ui/ChangeLog177-183 src/scave/ChangeLog125-127

Sources: src/sim/ChangeLog14-23 src/envir/ChangeLog5-8 ui/ChangeLog85-93 src/scave/ChangeLog125-127

Key Design Principles

Modular Structure: Behavior is implemented in C++ simple modules, while topology is defined in NED doc/src/manual/ch-simple-modules.tex6-11
Simulation Time Integrity: Uses fixed-point SimTime to prevent rounding errors common with floating-point types doc/src/manual/ch-simple-modules.tex154-156
Extensibility: Users can plug in custom RNG managers (cIRngManager), configuration providers, or event schedulers include/omnetpp/ChangeLog31-34 src/envir/ChangeLog183-185
Introspection: Every object supports metadata via cClassDescriptor, enabling runtime inspection in Qtenv include/omnetpp/ChangeLog69-72

Sources: doc/src/manual/ch-simple-modules.tex6-11 doc/src/manual/ch-simple-modules.tex154-156 include/omnetpp/ChangeLog31-34 include/omnetpp/ChangeLog69-72 src/envir/ChangeLog183-185

Next Steps

For detailed information, please refer to the following child pages:

Getting Started and Installation — Platform-specific setup (Linux, macOS, Windows, NixOS) and environment configuration using setenv and install.sh src/utils/ChangeLog16-18
Sample Simulations and Tutorials — Learning from the bundled examples like TicToc, Aloha, FIFO, and OSG demos .gitignore82-126

Sources: src/utils/ChangeLog16-18 .gitignore82-126