IHL

 
Introduction

In contrast to other field trials in Germany, the Universities of Mannheim, Freiburg, Karlsruhe and Heidelberg have been cooperating since 1995 in various teleteaching projects. Lectures, seminars, and exercises are exchanged on a regular basis. Audio, video, and slides (i.e., whiteboard data) of these courses are transmitted via multicast technology over the Internet/MBone. Therefore the number of participants is not restricted and it is even possible for students to take part in teleteaching sessions at home (a scenario called Interactive Home Learning IHL). 

However, one major condition is the high network bandwidth that is needed to transmit the media streams (audio, video, and whiteboard data) in sufficient quality. Experiences gained during a field trial realized by the University of Mannheim have shown that the limited bandwidth (128 Kbit/s) of standard ISDN connections causes poor reception quality, thus diminishing the acceptance of teleteaching by remote students.

Since ISDN does not offer a multicast service, a special dial-in gateway developed at the University of Mannheim is used. This gateway enables ISDN lines to be connected to multicast sessions and realizes scaling of the transmitted media streams (especially video) in order to adapt them to the lower bandwidth. The gateway is implemented mostly in Java and has a client-server architecture, whereby participants connect via the client to the server that is a member of the multicast group. Communication between client and server is based on RTSP (Real-Time Streaming Protocol). The transmission rate of both audio and video data is adapted to the ISDN bandwidth, prioritizing whiteboard data before audio before video. Furthermore, whiteboard data is buffered at the server to compensate for lost packets. 

One promising technology to overcome the bandwidth limitations mentioned above is ADSL (Asymmetric Digital Subscriber Line). Since February 1998, NEC, Deutsche Telekom, and the University of Aachen have been cooperating in a joint project to connect institutes and home users via ADSL to the network of the University of Aachen. Currently, 700 employees and students have access to the high speed network.

Synchronous teleteaching has not been tested in Aachen thus far, since on the one hand efficient multicast technology is lacking and on the other hand the University of Aachen does not offer synchronous teleteaching.
 

Project IHL

It is planned to transmit synchronous teleteaching courses held at the Univerity of Mannheim and/or Freiburg to the University of Aachen (e.g., Mannheim's "Multimedia Technik" lecture), using ADSL connections to enable the participation of students at home. While the degree of interaction in lectures is rather low, the cooperation between distributed participants is more pronounced in seminars and exercises. 

A 3 MBit/s ATM line will be established between Mannheim and Aachen. The ADSL connections in Aachen offer up to 8 MBit/s. Therefore an acceptable transmission quality of audio, video, and whiteboard data is given. 

The IHL project within ANETTE will be carried out by the Universities of Aachen and Mannheim in cooperation with NEC Europe. It has the following aims:

• To develop an efficient multicast service for ADSL based on multicast IP: ADSL Multicast Access Server.
• To test and enhance gateways and media scaling filters.
• A field trial with up to 24 students located in Aachen will be executed in order to evaluate ADSL in interactive teleteaching scenarios.
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