The one of challenges in VoIP networks development is how to manage network traffics. The reason for the challenge is VoIP traffics have to use Internet networks to bring their messages. Meanwhile, Internet is convergent networks which are very busy, because many applications use the Internet. The implementation of queuing mechanisms which can distinguish network traffics is the one of mechanisms to manage network traffics. PQ and CBQ are mechanisms which can divide traffics into different classes by using a priority mechanism. In this paper, the analysing of VoIP performance and its QoS to manage its services are executed by PQ and CBQ simulation. The E-model which is introduced by ETSI and standardized by ITU-T through G.107 is used to predict the value of MOS (Mean Opinion Score) services. Then the MOS value results are used to find a better mechanism between PQ and CBQ queue system for managing VoIP traffics.