As the number of processing nodes on chip multi-processors (CMPs) keeps increasing, providing efficient communication with the on-chip interconnect becomes increasingly critical. With 32-core CMP designs on the drawing table of engineers, there is a demand for accurate simulation models that capture all the complexities and interactions of the different design layers including the application, operating system, cache hierarchy, coherency protocol, and other on-chip resources. These components cannot be modeled anymore in isolation as unpredicted performance anomalies may arise once all the system variables are taken into account. In this paper, we present a simulation framework for CMP systems, focusing our attention on the on-chip network. We show preliminary results for the choice of key network parameters (topology, flit size) with respect to the behavior and performance of applications running on top of different network configurations. This paper tries to convey the need for an overall CMP system simulator as a way to accurately characterize the actual behavior of the on-chip network.