非同步傳輸網路多點傳送主幹之桌上型虛擬教室系統

Abstract

現有的互動式遠距學教學及學習系統大都有下列三個特性:使用專線網路 、使用會 議型影像傳輸、需要專業的操作人員。這些特性的缺點是成本 太高,使用者操作不便,系 統的可攜性低。本篇論文將報告我們在交通大 學非同步傳輸網路實驗平台上以多點傳送 主幹為基礎所發展出的虛擬教 室系統。此虛擬教室系統藉由使用分享式非同步傳輸區域 網路或網際網 路、桌上型的製作、使用軟體控制等特性，改善上述現有的互動式遠距學 教學及學習系統的缺點。 這個系統提供一個遠距教學及學習的環境讓相隔兩地的開課者(老師)及參 與者(學 生)彼此相互連繫起來。開課者可以開一堂課讓參與者加入並 將影像及聲音多點傳輸給 所有課堂上的所有參與者，使參與者能從自 己的螢幕及喇叭看到並聽到開課者。我們設 計了一個課堂控制協定讓開 課者控制參與者進入該課堂及傳輸影像的行為。因此，此系 統允許數十 甚至上百人同時加入一個堂課,此因此可以應付實際課堂的需要。 此外，這篇論文在多點傳送主幹的多點傳送路由協定方面亦有研究。我們 首先針對 "距離向量多點傳送路由協定"作說明，然後我們會提出此協定 的改進方法來降低網路成 本。 Most of interactive distant teaching and learning systems that already existtoday have the following characteristics: dedicated networks, room-based videoconferencing, and professional equipment operators, which are all costly and lack of in user- friendliness and portability. This paper reports our efforts in developing a MBone-based Virtual Classroom[1] system over the NCTU ATM testbed which eliminates the above three characteristics by a shared ATM LAN or Internet, a desktop implementation, and a software-controlled environment. This system provides a distant teaching and learning environment in which chairmen (teachers) and participants(students) can be connected remotely from their own workstation sites. The chairman can create a class session for participants to join and multicast his or her video/audio to all participants in this session so that participants can see/hear the chairman's video/audio from their monitors and speakers. A Class Session Control Protocol is developed to allow the chairman of a session to control the class entrance and video/audio sending of participants in this session. As a result, tens or even hundreds of participants may enter one class session which means our system is scalable and applicable in the practical environment. Moreover, a research on the multicast routing protocols of the MBone is also put in this thesis. We first have a survey of the Distance Vector Multicast Routing Protocol and then propose a modified method of the DVMRP to decrease the network cost.