Introduction

In the specialized literature the simulations are divided as follows:

1. Live simulation – real people operate real systems under real conditions. An example would be military exercises with troops in the field: personnel, equipment, logistical support and real medical insurance, real environmental conditions, and subsistence.

2. Virtual simulation – real people operate virtual systems under virtual conditions, but virtual conditions are programmed (created) by real people. An example is the training of pilots on simulation systems, in weather and visibility conditions artificially created by instructors (real people); the GSN_SIM simulator is also one of those serious games that fall within the specifications of a virtual simulation.

3. Constructive simulation – virtual people operate virtual systems under virtual conditions, but the scenario is built by real people and the behavior of virtual people is set by real people. JCATS is the tool used for training commands, staff, checking and testing standard operating procedures, the analysis of various courses of action etc.

4. Distributed simulation – synthetic environment designed to ensure real-time data exchange between different stand-alone simulation applications. In the virtual battlefield a whole “palette” of simulation systems is used. They are interconnected and standardized on a common platform to speak a “common language”.

Multilevel simulation is a federation model, a connection between constructive, virtual, and real simulations. That connection is done with High Level Architecture (HLA).

There are five important concepts regarding HLA:

1. Runtime Infrastructure (RTI) - send and receive data right to the receiver;

2. The Federate - interconnects a simulator to the RTI;

3. A federated HLA is described by a Simulation Object Model (SOM) - interface of a federation in terms of the data it generates as outputs and the data it requests as inputs;

4. The HLA Federation is a set of federations that are used to build a simulation and are all federated together with the RTI;

5. The Federation Execution is a session in which the federation runs.