Architecture of ePresence

ePresence is an Orchestrated Hypermedia Presentation System (OHPS) meant for pedagogic applications (such as Instruction-on-Demand). A teacher uses the tool-kit provided by this system, just like using the black-board or the over-head projection system, to create multi-media intensive lecture presentations. Once created and stored in an Instruction-on-Demand Server, students can interactively playback the presentation in real-time over the Internet using a typical web browser. The unique proposition about ePresence, over other several existing systems such as in [1][2] and [9], is that the ‘pointer synchronization’, ‘delivery’ and ‘user’s participation’ are all handled in real-time. This is achieved using a SGML based media representation format and a master-slave synchronizer to capture, store and restore the pointer synchronization at the source (teacher’s end) and destination (student’s end) respectively. Besides this, a two-channel approach is used in delivering the media objects and also handling the user’s participation in an orchestrated communication to achieve the real-time communication. In this paper, we describe the architecture of ePresence, discuss the prototype implementation and demonstrate its use in pedagogy. 1 Orchestrated Hypermedia Presentation Systems for Pedagogy Orchestrated Hypermedia Presentation Systems (OHPS) are designed to implement applications such as News-on-Demand, Music-on-Demand, Movies-on-Demand and Instruction-on-Demand over the World Wide Web (WWW). Two notable design requirements of an OHPS are the granularity of synchronization between the media elements and the modes of interaction that are made available to the user [6]. For example, information/recreation applications (e.g., News, Music and Movies-onDemand) require lip synchronization and perhaps VCR mode of interaction, whereas educational applications (such as Instruction-on-Demand) require pointer synchronization and hyperlink based interactivity. An ideal OHPS for pedagogic environment is one that incorporates pointer synchronization between media elements, provides hyperlink based interactivity and delivers media elements in real-time (on-line). In OHPS, while the synchronization between media elements is represented using a mark-up language, the delivery and the mode of interaction are guided/influenced by the protocol used for communication. OHPSs implemented using existing WWW standards such as HTML-HTTP Author for Future Correspondence (for hypertext applications) and SMIL-RTSP (for hypermedia applications) fail to satisfy more than one requirement of an ideal OHPS. Several other implementations have addressed only two of the three requirements. In this paper, we discuss all the three requirements that make our OHPS more suitable for pedagogic environments. The OHPS environment in this paper is based on the ePresence architecture, which consists of: an SGML based media representation format for synchronization between media elements, a master-slave synchronizer at the client end to achieve pointer synchronization, and a two-channel approach to deliver media elements in real-time providing hyperlink based interactivity to the user. A prototype implementation of an OHPS (named ePresence) with these three properties has been completed and a sample presentation is made available at [11]. The rest of the paper is organized as follows. In the next section we describe the issues in designing an OHPS for pedagogy. In section 3, we briefly list out the existing implementations of OHPS for pedagogy and emphasize the need for a new system that would address all the requirements of an pedagogic environment. The architecture and the prototype implementation of our proposed new system, namely, ePresence is discussed in section 4 and the paper is concluded in section 5 with a qualitative comparison of this system vis-a-vis other systems. 2 Design Issues in OHPS 2.1 Application Model EDIT STORE STOP START