REIHE INFORMATIK 498/98 A Multicast Gateway for Dial-In Lines


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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