In current Master thesis we present NetSim, a service for automatically generating simulations using the Castalia Network Simulator. NetSim was developed as part of an integrated Wireless Sensor Network design platform. We introduce the Network Simulation Descriptor (NSD) Model which integrates all the information necessary for defining, configuring and executing a simulation job, in a single model. The NSD model can be easily enhanced, manipulated and configured during design and runtime, causing the minimum programming effort as far as it concerns 1) the integration process with the rest platform tools and 2) the automated mapping process to the Castalia Network Simulator. NetSim is characterized by a model oriented programming philosophy, which abstracts new software specification definitions, their development process and their integration with the existing software, from great changes to the already developed software architecture and functionality. NetSim's Model driven programming design and philosophy offers great flexibility and customization abilities to the developed software, which makes further development of the existing software simple and straightforward.