There have been various reliable multicast protocols now

but they can’t satisfy special real-time requirement in applications

that is

before new data reach continuously in a certain time step the old data must be recovered

otherwise

the old data are invalidated.A real time reliable multicast protocol is put forward for the special application requirement.It takes techniques of hybrid FEC

hierarchical network local recovery and an active NAK mechanism to control and reduce the recovery time effectively

and use NAK suppression mechanism to preserve its high scalability.For evaluating the performance of the protocol

the processing and recovery procedure delays in the node and end-system are quantitated accurately through the Passion theory on the basis of modeling the protocol communication in this paper.Then the transport delay calculating formula is presented.The simulated results show the transport delay of the protocol has good robustness and scalability.