Scalability in reliable multicast communications is a primal requirement, since there is a large growth of distributed applications based on internetworking with global dimensions. This paper proposes a priority scheme applied to three reliable multicast protocols, resulting in different generic models and performance evaluation for these models is established. The results show that the priority scheme ensures more robustness when possible variations of network states take place. There is a slight difference for the mean delay experimented under this scheme, when an increase in loss probability or in network load occurs. The mean delay has also little sensibility due to raise of number of participants in the multicast system.