As the demands for multicast multimedia applications, e.g., multiparty video conference, increase rapidly, it is urgently required to provide a feasible multicast communication environment and the corresponding multimedia presentation control schemes. In this paper, we propose a Multipoint Multimedia Service Network (M3SN) to achieve multicast multimedia presentations. A M3SN consists of a lot of LANs and a WAN. Each LAN is serviced by a multimedia server. The concept of 'virtual server' is adopted in M3SN. The physical server, which stores media sources that are requested by a group of clients locating in different LANs Li, i = 1...k, multicasts media units to servers of Li. Since servers of Li, i = 1...k, play the role of media relays, i.e., receiving media units from the physical server and then multicasting received media units to the clients that are in Li and request the same media resources, servers of Li are called 'virtual servers'. Some jitter may occur when media units traverse across the WAN. A virtual server adopts some synchronization control schemes to smooth the occurred jitter. In this way, the clients that are located at the same LAN do not need to deal with the occurred jitter individually. We apply Extended Finite State Machines (EFSM) to formally specify multimedia synchronization in M3SN. Based on the EFSM model, intra-medium synchronization is handled by an Actor EFSM; inter-media synchronization is handled by a Synchronizer EFSM. Synchronizer and Actors cooperatively achieve smooth multicast multimedia presentations in M3SN.
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