NetLab -- an interactive simulation environment for communication networks. Today the need for developing special simulation software for the modeling and study of communication networks has become vital. This paper presents a new simulation environment for the design and study of communication networks called Network Laboratory, or simply NetLab, laying special emphasis on centralised network design, tree network design and routing in networks. It is destined for educational use inside the academic community, as part of a course in networks. The software, designed to run under both Linux and Windows 9x/2000/NT/XP, is implemented using Tcl/Tk, a high-level scripting language. A comparison of the characteristics of Netlab with the characteristics of other tools like the Kershenbaum design tool and the ns tool, brings out its many capabilities and points of superiority in terms of simplicity, user friendliness and intelligence.