In spite of the progress made in the past decade, the quality-of-services (QoS) of the video-conferencing (VC) systems involving four or more sites need to be improved much further in order to attract a large number of users. One of the key issues in enabling high-level QoS in multi-party (MP) VC systems is the accurate maintenance of the temporal relationship among media units (MUs) from creation to play while keeping the MU delivery delays within acceptable bounds. Unlike the case of two-party video-conferencing, MP VC requires multiple media streams to be delivered to multiple sites with a high degree of synchrony. In this paper, an MP VC system model called the SB-VC system in which a global-time-based synchronization approach called the target play time (TPT) scheme is used is presented. The TPT scheme is highly effective in achieving high-precision intra-stream, inter-stream, and inter-destination synchronizations in MP VC. As a validation, a prototype SB-VC system has been constructed by use of the Time-triggered Message-triggered Object (TMO) specification and programming scheme and its tool-kit. Its performance is compared against that of an advanced research prototype developed by Microsoft, ConferenceXP, and the results demonstrate that the SB-VC system is a promising model for realizing next-generation VC systems that offer QoSs significantly better than those of current-generation VC systems.