This work presents a planning methodology for multimedia networks based on a hybrid traffic model and an evolutionary optimization procedure. The methodology intends to optimize the sizing of network elements to comply with two QoS simultaneous network parameters as well as to promote network stability and cost efficiency. The hybrid traffic model deals with the multimedia network traffic as a combination of fBm (fractional Brownian motion) and Markovian process. Also, the model considers the links loads and variance coefficients to produce more accurate Qos metrics values for network delay and packet loss probability. The traffic model characterization accuracy was evaluated with an optimization procedure that sizes network elements to fulfill performance and cost requirements. The simulation's results show that the methodology may have a practical use for sizing network elements and promoting stability.