MEDIA SYNCHRONIZATION IN HETEROGENEOUS NETWORKS - STORED MEDIA CASE

This paper studies a set of lip synchronization mechanisms for heterog eneous network environments. The set consists of four schemes, types 0 through 3, which are classified into the single-stream approach and t he multi-stream approach. Types 0 and 1 belong to the single-stream ap proach, which interleaves voice and video to form a single transport s tream for transmission. On the other hand, types 2 and 3, both of whic h are the multi-stream approach, set up separate transport streams for the individual media streams. Types 0 and 2 do not exert synchronizat ion control at the destination, while types 1 and 3 do. We first discu ss the features of each type in terms of networks intended for use, re quired synchronization quality of each medium, physical locations of m edia sources and implementation complexity. Then, a synchronization al gorithm, which is referred to as the virtual-time rendering (VTR) algo rithm, is specified for stored media; MPEG video and voice are conside red in this paper. We implemented the four types on an ATM LAN and on an interconnected ATM-wireless LAN under the TCP protocol. The mean sq uare error of synchronization, total pause time, throughput and total output time were measured in each of the two networks. We compare the measured performance among the four types to find out which one is the most suitable for a given condition of the underlying communication n etwork and traffic.