On a basic level, a network simulator uses mathematical formulas to create a theoretical and entirely virtual model of a network. Simulators are software solutions and different types are available for different applications. While used primarily for research and educational purposes, they can also act as crucial testing tools in the design and development of a network.
Simulators, such as ns-3, are used to simulate networking and routing protocols. OPNET, which was acquired by Riverbed in 2012 and applied to their SteelCentral product line, also provided a standalone simulation environment.
Both of these network simulators use discrete event simulation which chronologically queues and processes events like data flow. This allows a network architect or engineer to build and evaluate an experimental model of a network, including its topology and application flow. Since a variety of theoretical scenarios can be introduced to a network where anything can be built and applied, performance can be hypothesized before the network itself has even been implemented within the real-world.
Although testing a network in such a manner can save both time and money, network simulators aren’t without their limitations. These highly complex operations require a degree of experience and training to properly configure in order to acquire reliable results. Additionally, network simulators just aren’t practical in that certain events can’t be anticipated independently of a physical network.