ISTOS (Iowa State Optical Simulator) is an advanced tool for simulating fiber optic networks. It is currently being developed at the Dependable Computing & Networking Laboratory at Iowa State University.

ISTOS consists of a front-end GUI which runs on Windows on .NET framework and a back-end simulation-engine which runs in both Windows and Linux environment. ISTOS GUI provides a user the ability to draw a physical network topology and set different parameters of the links (such as delay, bandwidth, jitter, bit-error rate) and the nodes (wavelength-timeslot conversion capabilities, switching capabilities) in the network to be simulated.
The ISTOS back-end simulation engine can currently run on the same Windows machine as its GUI or on a separate Linux machine. The underlying physical topology along with its different set parameters and configuration files are passed to the back-end simulator running over Linux using Secure-Shell (SSH) sockets. The simulations are triggered at the back-end with the set parameters and the user has the optional capability to pause, replay and terminate the simulation at any point of time. Once the simulations are completed, the results of the simulations are reported back to the front-end GUI using the SSH sockets, and different statistical analysis is done to compute different performance metrics associated with an optical network.

In summary, ISTOS enables the user to do the following:
• Create multiple experiments. An experiment is a group of network topologies with the same connectivity, but varying link and/or node properties. A simulation is run on a single experiment at a time.
• Define simulation parameters which include the duration of the simulation, the traffic arrival rates, and the parameters of the traffic arrival distribution function.
• Specify fault-injection mode and rate and fault recovery strategy to study fault recovery management in optical networks.
• Specify node, link and routing strategy(shortest path, minimum hop, widest-shortest path, least congested path, shortest-widest path) for each network topology.
• Simultaneously simulate network traffic (between different source-destination pairs) on all network topologies within one experiment.
• Create automatic breakpoints or manual pause/re-play to view the states of each network topology in terms of traffic requests at any point during the simulation.
• Comparative study of the performance of different networks by analyzing the simulation statistics for each network generated at the completion of the simulation.