Abstract: Layered multicast has been proposed as a solution to video multicast over Internet. Existing multicast protocols usually perform layer adaptation at the receiver’s side,using static layer rate allocation techniques at the sender’s side. In this paper,the basic theory of layered multicast is introduced firstly. The technology of receiver-driven fixed layer rate allocation and dynamic sender-driven rate allocation is discussed. Especially,a kind of metric,called utility,is introduced to measure the satisfaction with the multimedia application. An optimal rate allocation algorithm based on system utility,ORAU,is brought forward. Then a solution to the allocation algorithm is found through ratiocinating and proving. Subsequently,the implementation of ORAU algorithm is presented. Finally,ORAU algorithm is simulated in specific network environment. The results of simulation are compared with other algorithms,such as GAU and SLM. They show that the multimedia multicast system adopting ORAU algorithm can gain higher utility with little bandwidth cost. Thus the feasibility and effectivity of the algorithm are verified by the results of experiment and simulation.