In OMNeT++, a Network is an object that defines the network and holds modules, submodules, and compound modules. The Network object allows those different types of modules to talk to each other via channels.

When you run your network simulation, the Network object will look like the following:

I have called this Network object My_Network.

A Module object in OMNeT++ is a component that sits inside a Network object and is able to send messages to other Module objects. In your simulation, this could be a router, a webserver, a standalone machine, or any other component that you can think of, which is capable of making the communication across a network. When we add a Module object to our My_Network Network object, it looks like the following:

I have named the module My_Module and you can see that it sits inside the My_Network Network object, as shown in the following screenshot:

A Compound Module object is made up of multiple Module objects. The INET simulation framework for OMNeT++ is a library that contains loads of prebuilt Module and Compound Module objects. The following is what a StandardHost Compound Module looks like inside our My_Network Network object:

INET provides a neat icon for the StandardHost Compound Module object. If we have a look at what makes up this object, we can see a collection of Module and Compound Module objects that together make up a typical or "standard" host that you would find on a real-life network. The following is what the StandardHost Compound Module object looks like under the trunk:

Note the modules such as TCP and UDP; these prebuilt components are all ready for use and at your disposal! We can also see that the StandardHost Compound Module has a module inside it titled pingApp. This is an instantiation of the iPingApp Module Interface and it allows StandardHost to be used as a ping application and thereby send pings to other nodes on the network as shown in the following screenshot:

Channels are objects that are used to connect one module of the Compound Module object to the other. Channels allow these modules to send messages to each other and connect the gate of one module to the gate of another. This could be a StandardHost talking to another StandardHost via an Ethernet cable.