In this paper we describe our experience in performance evaluation of CMP-based VoIP SPS (signaling parse system). We also present a performance model of the system using GI/G/m-FCFS multi-class open QNs(queuing networks). And deal with approximate performance analysis of open non-product-form QNs, based on the method of decomposition. Our approach predicts the major performance evaluation parameters of the system under the workloads and also identifies bottlenecks in the system. Performance results are inserted back into the QN model as initial values associated to the relevant model elements. The theoretical estimates are shown to be in excellent consistence with testing results. It shows the effectiveness of the proposed model. This work explores performance issues of CMP-based applications by means of performance modeling. In this way we may get an immediate feedback on the system performances. The use of QN model allows us to achieve better multi-core application performance.