With the increasing number of MBone sessions the interest of home users to participate is also increasing. Unfortunately the cost for the hardware necessary to participate in multicast sessions over a high speed link are still prohibitively high. In our Interactive Home Learning project are providing methods to participate in a teleteaching lecture – transmitted on the MBone – live from a PC at home via a low-bandwidth connection (e.g. ISDN). This paper discusses technical problems and solutions for users who wish to participate in multicast sessions over dial-in lines and presents our approach, the ISDN Multicast Gateway, which meets the requirements for an application layer multicast router with a very restrictive broadcasting policy and a dynamic tunnelling mechanism. The ISDN Multicast Gateway allows the transmission of selected multicast sessions over dial-in connections such as ISDN by providing a mechanism to configure a multicast tunnnel dynamically. For each selected media stream the desired quality of service parameters can be set interactively, e.g. a certain share of the available bandwidth can be reserved. In order to allow a graceful scaling of video we integrated a simple scaling mechanism for H.261 video streams that controls the temporal resolution of the video.
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