Abstract. Commercial Off The Shelf (COTS) modeling and simulation tools are now available that are capable of automating many of the time-consuming systems engineering processes employed to design and optimize Wide Area Networks (WANs). Because WANs continue to evolve and increase in complexity, automated modeling and simulation tools are now required to effectively perform design and optimization analyses. Through the use of modeling and simulation tools, systems engineers can generate WAN designs with lower costs, greater accuracy, and in a shorter amount of time than was previously possible. Ideally, one engineering tool would be utilized to solve all network design problems for all types of communications networks. Unfortunately, such a tool does not currently exist. Thus, the most pragmatic approach is for systems engineering organizations to select and integrate a multitude of COTS WAN modeling and simulation products that can interface and work harmoniously together.