Virtual Tele-Education and ATM-based Networks
D. N. KANELLOPOULOS*, A. MALATARAS*, L. MANDALOS*, I. MOUNTZOURIS*, S. KOUBIAS*, G. PAPADOPOULOS* *
Applied Electronics Laboratory, Department of Electrical Engineering & Computer Technology University of Patras, PATRAS 26500, Greece tel: +30 61 997 312. fax: +30 61 997 333. e-mail:
[email protected]
Abstract In this paper, a consideration about the notions of “virtual classroom” and “virtual education” is forwarded. Although, most of the current tele-education systems use ISDN (Integrated Services Digital Networks) and satellite lines, the successful development of tele-education services depends on the deployment of high-speed networks to transfer multimedia traffic. In this article, dominant network technologies which are used as infrastructure for tele-education systems are presented. These technologies are: Frame Relay, Distributed Queue Dual Bus, Switched Multi-Megabit Data Service, Fibre Distributed Data Interface, FDDI-II, Synchronous Optical Network and Asynchronous Transfer Mode (ATM). The disadvantages of these high-speed network technologies are addressed and it is elucidated for which reasons, ATM technology is the solution for implementing multimedia networks. Next, European projects for tele-education network infrastructure are presented. Moreover, tele-education products are discussed and products for video conferencing systems are mentioned in brief.
INTRODUCTION Nowadays, more than eighty (80) academic research projects have produced systems, which offer virtual lessons [1] with the usage of Computer Mediated Communications. Consequently, virtual students have the ability through the tele-education services to choose: subject of knowledge, educator, time, place, level, rate, and way of education, as well as the media applied in the educational procedures. For instance, in the New Jersey Institute of Technology, a “virtual classroom” operates since 1986.
1. Virtual Learning Virtual learning is a new model of distant learning, in which many educational procedures become feasible without the direct human communication between educator and apprentice. In virtual learning environment, an educator can intervene in the study material (e.g. to make appendixes, modifications, deletions), and the student can communicate with the educator as well as with other students. The study material, which is expressed in hypertext format, is renovated and exploits the nature of multimedia data presentations [2, 6] (e.g. text, graphics, pictures, animation, shared mouse pointer coordinates, voice, audio and video). 2. Networking Requirements of Tele-Education Applications Tele-education applications are characterized by the integration of multiple streams of different media types, which have different data requirements (i.e. storage capacity) and different requirements regarding transport performance and characteristics. The end-user of a tele-education application must be able to handle multimedia objects, consisting of synchronized information of different media. Since, an extensive study of the networking requirements, imposed by tele-education applications is out of the scope of the paper, due to limited paper length, a concise table is given. Table I lists requirements [7-9] imposed by multimedia applications in lower layers of Open Systems Interconnection Reference Model (OSIRM). 3. Networking infrastructure issues In a tele-education environment, the communication problem is to access, address, manage and manipulate multimedia data (e.g. text, images, video, audio, moving images). Networking infrastructure plays an important role in the establishment of tele-education systems, since teleeducation services generate multimedia traffic [2, 6] in a LAN or WAN environment. Actually, a tele-education system must be capable of addressing multimedia requirements and providing remote tele-education services to its users. A network infrastructure must provide functions for isochronous and asynchronous transmission, conference management and a standard broadband network interface, in order the service user (e.g. an educator or a novice) to participate in group-working processes. For the above reasons, an exploration for suitable networking infrastructures in the tele-education area is indispensable. The remainder of this paper is organized as follows. Next section discusses high speed network technologies capable of supporting tele-education services. Section 3 addresses ATM benefits in the tele-education environment, while Section 4 presents European projects for tele-
education network infrastructure as well as, some ATM-based network trials in the multimedia area. Finally, concluding remarks are given in last section. Table I. Requirements imposed by distributed multimedia applications Physical network requirements (OSIRM layers 1-2) Dynamic Bandwidth Management
Bounded Delay, and Bounded Delay Variance
Bounded Error Rate
Proper transmission services
Out of-band signalling
Short description
Transport service requirements (OSIRM layers 1-4)
Bandwidth>100Mbits/s
The end-to-end delay and end-to-end jitter must be bounded in order to have guaranteed QoS services. BER
