Realization of Control and Management Capability for Interactive Group Communication Systems over Wide-Area Internet/ATM Networks

• Main Authors: Chorng-Horng Yang, 楊崇宏
• Other Authors: Kim-Joan Chen
• Format: Others
• Language: en_US
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/77339540375384711022

博士 === 國立中正大學 === 電機工程研究所 === 89 === As the new computing and networking technologies emerge, communications have gradually evolved from the point-to-point data communication to the interactive multipoint multimedia communication. With the support of interactive multipoint multimedia communications, many advanced interactive multimedia applications and systems, such as distance learning and videoconferencing, are becoming feasible. However, since the users of such applications and systems, which are deployed in an internetworking environment, demand for more versatile multimedia services and more advanced control and management functions, researchers, thus, constantly face new challenges and have to deal with many new technical issues when they develop such a system. In this dissertation, we address the realization of control and management capability of interactive group communication systems over Internet and ATM (Asynchronous Transfer Mode) networks. An ATM network can support distribution of high-quality audio and video over a wide geographical area. On the other hand, the Internet, which is more popular and cost-effective, is used for gathering user’s interaction requests. Users of the interactive group communication system, in general, operate the system according to some specific interaction behavior. They issue requests through the Internet, and the system collects these requests to process and, then, generates corresponding control scenarios. Each control scenario involves many control instructions, which are sent to and executed by the multimedia devices to accomplish multimedia distribution or, in the other words, interactive group communications. In order to explore the complicated control and management behavior and evaluate the control and management capability of such a group communication system, we developed an ATM-based videoconferencing (AMV) system, which is built on a commercial multimedia distribution system and is capable of supporting several conference control and management functions. Through running this prototype system, we can further investigate its control and management capability. The prototype AMV system can support continuous presence with high-quality audio/video and provide conferees with conference control, floor control and status report. We adopt Web-based control and management by developing the Web-based control interfaces and a Web server. Conferees can initiate requests for conference and floor controls at their Web browsers and obtain every conferee’s status easily through the Web browser. As for the system control, a centralized server is responsible for controlling and coordinating the distributed multimedia devices. This server processes the conferees’ requests and distributes corresponding control instructions, through ATM networks, to multimedia devices, which execute the instructions to accomplish the interactive group communication. We deployed and experimented the AMV system in Taiwan experimental ATM network and Taiwan Academic Network (TANet), and obtained many valuable experience and experiment results. To explore the complex control and coordination behavior, we propose a model to capture four control abstractions: conferee interaction, coordination of control/management operation, distributed control flows, and control message dispatch. Our study shows that the message dispatch involves higher risks of violating the control and coordination due to the asynchrony of communication networks. To resolve the control and coordination issues, we enhance a causal multicast to send various types of control messages, so that the integrated control can be achieved. Besides, we also investigate the impact of the unpredictable response time and the asynchrony of the Web-based control interfaces, and discuss approaches for solving the problems of the Web-based control interfaces. We also evaluate the proposed disciplines for floor competition, and analyze the response time of conference control. In order to evaluate and further optimize the control and management capability of the system, we propose a videoconference model, and then define the performance metrics, interactivity and controllability, and derive stability constraints. Unfortunately, increasing the interactivity would degrade the system controllability and stability. On the other hand, to obtain a higher controllability may sacrifice interactivity. We thus formulate these performance issues as optimizing both of the interactivity and controllability subject to stability constraints. In other words, an interactive group communication system that has good control and management capability can achieve both higher interactivity and higher controllability and meet the stability constraints. To resolve these optimization problems, we develop some approaches, which can dynamically adjust, according to network conditions, the system parameters to achieve higher controllability and interactivity. In addition to tuning system parameters dynamically to optimize the performance, we develop a causal-ordering group communication protocol to support multicasting control messages over wide-area networks and thus improve the control and management capability. Existing causal ordering protocols adopt the approach of passively ordering messages at receivers. However, these protocols may suffer from buffer overflow when they are used by highly interactive multimedia applications. We develop an adaptive message scheduling approach to resolve this issue. So, the proposed group communication protocol can successfully multicast the control messages with respect to causal ordering and thus can effectively improve the control and management capability. The major contributions of this work include (i) design and realize the control and management capability of an interactive group communication system, (ii) analyze the complicated control and coordination behavior, (iii) evaluate and optimize the system performance, and (iv) propose approaches and protocols to improve the control and management capability. For future works, researchers may explore the highly interactive multimedia group communication services with many different quality-of-services. The future research topics may include layered video through multicast channel, differential services, multicast protocols, large-scale group communications within a hierarchical structure, etc.