This paper presents a network-on-chip transaction simulator with the aim of providing early performance estimation for a given application. The simulator is an example of communication centric simulation and requires reduced characterization of a given system to provide performance results. It incorporates spatial access patterns and device response speeds to accommodate a wide range of embedded system instances, as well as accurate behavioral modeling of transaction types for on-chip components. To demonstrate the performance estimation capabilities of the simulator, an MPEG-4 decoder is modeled and various performance results are obtained.