Time - Line : A Network Protocol

Time-Line: A Network Protocol for 1.1 The CAL Application Network Multimedia Supporting A CAL application is being developed which will be used Classroom-Based CAL as a part of the taught medical course at the Forester Hill Medical School during 1997. The application takes the Dr Godred Fairhurst1, Dr Nihal Samaraweera1, Steven. student through a series of high quality video clips Pavett2 Dr Neil Hamilton2. recorded in MPEG-2 format. Each clip is interspersed by graphics and text-based material with questions. Students Abstract are also presented with the option to read additional material relating to the subject. Although the material is This paper describes the initial results of a study structured around a sequential set of video clips, the investigating the practical issues in delivering clips of student has control over which clips are to be viewed and high quality digital video as a part of a medical Computer the level of detail presented. In a typical scenario, a Aided Learning (CAL) application. The application student will view five to six of the eight video clips in delivers interactive multimedia to one or more classrooms the current exercise. Each clip is approximately 10 from a network server connected via a wide bandwidth minutes in length (i.e. hundreds of MB of data). Metropolitan Area Network (MAN) which is further connected to other remote sites via a Wide Area Network One of the essential properties of CAL is that students (WAN). MPEG2 compression is used to encode the proceed at their own speed through the material, and may medical teaching material (a range of MPEG encoding take the opportunity to review previously viewed video strategies will also be compared as a part of the project). clips and follow optional material. None-the-less, there is still significant structure concerning the order in This paper considers the network aspects of the which the material is viewed. There is also some application, and describes the issues which were examined commonality between the video clips which are viewed during the development of the network protocols, known by different students performing the same exercise. This as the “Timeline service”. This uses a novel session is in stark contrast to the essentially random viewing of protocol to overcome the performance bottlenecks WWW material, and is a property which the Timeline encountered when supporting a large number of clients service will seek to exploit. across a network, by exploiting the commonality between the client requests for video clips when used in a CAL The system consists of a number of components (Figure classroom. Particular emphasis is placed on the 1). At the client, each user uses a web browser to view fundamental issues concerning the design of the protocol the WWW material which contains a Java applet to and the problems which were encountered. manage presentation of the video clips.