Real-time Synchronization Model Research Articles

Digital twin-enabled real-time synchronization for planning, scheduling, and execution in precast on-site assembly

Planning, scheduling, and execution (PSE) are essential for coordinating tasks during on-site assembly in prefabricated construction. Real-time synchronization supports collaborative decision making for planning and scheduling, and dynamic adjustment of execution in on-site assembly. However, simple and resilient mechanisms are lacking for on-site task allocation and performance in urban areas with limited buffers, and real-time information hasn't been fully used for automatic generation and adjustment of PSE. This paper proposes a digital twin-enabled real-time synchronization system (DT-SYNC), which aims to facilitate PSE using real-time resource status and construction progress information obtained from high-fidelity digital twins. Inspired by functional tickets in graduation ceremony, a real-time synchronization model with cyber-physical visibility and traceability is designed to organize and coordinate operations and resources with enhanced simplicity and resilience, which guarantees that appropriate resources are spatiotemporally allocated to appropriate activities. A numerical experiment and related robotic testbed demonstration are conducted for proof of concept.

Synchronization modeling and its application for SMIL2.0 presentations

A novel synchronization model namely Extended Real-Time Synchronization Model (E-RTSM) for modeling SMIL2.0 temporal behaviors is proposed in this paper. E-RTSM deals with event-based/non-deterministic synchronization as well as schedule-based synchronization in SMIL2.0. Converting of the temporal relationship of a SMIL2.0 document to E-RTSM is presented. Moreover, design of the E-RTSM-based data-retrieving engine for SMIL2.0 presentations is also proposed in the paper. The data-retrieving engine estimates the worst-case playback time of each object at the parsing stage and applying an error compensation mechanism at run-time to adjust the estimated playback time as well as the schedule of the fetching requests for data retrieval. Performance measurements from the real implementation of the E-RTSM-based data-retrieving engine for SMIL2.0 presentations have demonstrated the efficiency of the proposed technique.

Design and implementation of the just-in-time retrieving policy for schedule-based distributed multimedia presentations

In order to provide the smooth playback of a distributed multimedia presentation, the object-retrieving engine for the player must fetch each object before its playback time. In this paper, a smart object-retrieving engine is proposed, which adopts a retrieving policy named the just-in-time policy. The policy expects the retrieval process of an object to finish right before the playback time of the object to achieve a better buffer utilization and network bandwidth efficiency. The proposed object-retrieving engine focuses on SMIL1.0-based multimedia presentations. By converting the synchronization relationship of objects in the SMIL1.0 document to Real-Time Synchronization Model, which simplifies the handling of the synchronization relationship, and considering the end-to-end bandwidth as well as the user interactions, the object-retrieving engine determines the object request time for each object. The engine issues the request to fetch each object for the ongoing presentation at the object request time, and provides the player with proper media objects. The feasibility and better performance of the proposed just-in-time retrieving policy had been proved by performance measurements of system implementation.

SMILAuthor: An Authoring System for SMIL-Based Multimedia Presentations

In this paper, an authoring tool named SMILAuthor for SMIL-based multimedia presentations is proposed. SMILAuthor adopts standard SMIL language as the format of the presentation to generate reusable and easily accessible presentations. Moreover, powerful editing functions such as cut, copy, and paste are supported by the system in a timeline-based manner. In order to support timeline-based editing functions, the playback duration of each object in the input SMIL script is first calculated by the parsing process of the system. The parsing process extracts and converts the temporal relationship of the input script to Real-Time Synchronization Model (RTSM), and the playback duration of each object in the script is then computed by traversing the RTSM. Editing results are converted to the SMIL format and saved in the output file. Language structure of SMIL is hidden by the system and the temporal information is visualized in the timeline manner to provide users an easy way to understand and control the timing of each object. Implementation of the system provides a friendly WYSIWYG environment and multiple views/windows are provided by the system to help authors compose multimedia presentations efficiently.

A multimedia synchronization model and its implementation in transport protocols

An implementation of a synchronization mechanism in transport protocol to support multimedia applications over a packet or cell switched network is proposed. In designing such a mechanism for practical use, ease of implementation and capability of handling random delay of packets are two key issues for success. Since the random delay of packet or cell switched networks makes synchronization among media more complicated after the transmission across the network, a model which considers the random transmission delay is hence required to specify the temporal relationship among media. Therefore, a real-time synchronization model is presented to satisfy this requirement in the paper. Based on the proposed synchronization model, a transport protocol, namely the multimedia synchronization transport protocol (MSTP), is designed and implemented. We have implemented a prototype system using the MSTP protocol and built a simulation system for the wide area network (WAN) environment in order to evaluate the performance of the MSTP protocol.