Techniques for exploring global time and achieving high-level QoS in multi-party videoconferencing systems

Even though steadily growing in both variety and functional complexity, one of the key issues in enabling high-level QoS in multi-party videoconferencing (MPVC) systems is still the accurate maintenance of the temporal relationship among Media Units (MUs) without the loss of real-time performance required by the human perceptions. Ubiquitous two-way videoconferencing systems focus on synchronizations for one or two streams among two sites while multiple streams delivered to multiple sites need to be synchronized in MPVC. In this dissertation, the principle of global-time-based coordination of distributed actions (TCoDA) is exploited to form a fundamental and promising approach for solving this problem. An innovative global time-based synchronization technique (TPT scheme) based on this principle is proposed to provide high-precision intra-stream, inter-stream, and inter-destination synchronizations for MPVC.; Reducing the amount of efforts for designing and implementing MPVC while synchronizing various kinds of distributed actions to provide high-level QoS in MPVC has become another major challenge in the distributed real-time multimedia software research community. While the conventional remote method invocation mechanism has been considered for a long time as the primary high-level programming model for facilitating interactions among real-time objects in distributed systems, a multicast support mechanism has been recognized in recent years as an attractive supplement, if not a favored approach, in many applications. One highly promising concrete formulation of a multicast mechanism and an associated programming model is the real-time multicast and memory-replication channel (RMMC). This dissertation presents an API set designed for facilitating easy use of RMMCs and a middleware subsystem devised to support RMMCs.; As a validation, an MPVC with high-level QoS support is constructed with the use of the Time-triggered Message-triggered Object (TMO) scheme and its tool-kit, including RMMC. Its performance over Wide Area Network (WAN) demonstrates that TCoDA, including the TPT scheme, is a fundamental and promising approach for distributed multimedia applications. It is also a demonstration that the TMO scheme and its tool-kit (including RMMC), which enable relatively easy high-level programming of manipulations of global time-stamps and timely processing of MUs, are significantly helpful in reducing the amount of efforts for designing and implementing complex distributed multimedia applications.