EFSM-based continuous media synchronization in multicast networks

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 L_i, i = 1...k, multicasts media units to servers of L_i. Since servers of L_i, 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 L_i and request the same media resources, servers of L_i 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.