A Layered Approach to Simulating Communication Systems using Simula

In this paper we describe a Simula package (or `context') for simulating radio communication networks. The context is developed in layers, the higher layers in the context being patterned after the levels of the ISO/OSI Reference Model. Each of the layers in our context is developed as a separate subclass of the standard Simula class Simulation, and layers that model OSI levels include interfaces to adjacent layers. The context provides an easy-to-use interface to a model of the Physical Layer (Layer1) of the OSI model. Within Layer1 we provide models for several types of radio communication systems including spread spectrum transmitters and receivers. Users can redefine some of the attributes of the transmitters and receivers defined in Layer1 without the need to modify Layer1 itself. We illustrate our approach with the example of a radio network that uses a carrier-sense multiple-access protocol for channel access.