A Multipoint Data Communication Infrastructure for Standards-Based Teleconferencing Systems
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A Multipoint Data Communication Infrastructure for Standards-based Teleconferencing Systems vorg elegt von Diplom-Informatiker Jörg Ott Vom Fachbereich 13 − Infor matik − der Technischen Universität Berlin zur Erlangung des akademischen Grades Doktor-Ingenieur − Dr.-Ing. − genehmigte Dissertation Berlin 1997 D83 A Multipoint Data Communication Infrastructure for Standards-based Teleconferencing Systems vorg elegt von Diplom-Informatiker Jörg Ott Vom Fachbereich 13 − Infor matik − der Technischen Universität Berlin zur Erlangung des akademischen Grades Doktor-Ingenieur − Dr.-Ing. − genehmigte Dissertation Promotionsausschuß: Vorsitzender : Prof. Dr. rer. nat. Peter Pepper Ber ichter: Prof. Dr.-Ing. Sigram Schindler Prof. Dr.-Ing. Ute Bormann, Universität Bremen Tag der wissenschaftlichen Aussprache: 28. April 1997 Berlin 1997 D83 If, as it is said to be not unlikely in the near future, the principle of sight is applied to the telephone as well as that of sound, earth will be in truth a paradise, and distance will lose its enchantment by being abolished altogether. Arthur Mee, 1898 Zusammenfassung Ott, Jörg: A Multipoint Data Communication Infrastructure for Standards-based Teleconferencing Systems Eine Infrastruktur zur Mehrpunkt-Datenkommunikation in standardbasierten Telekonferenzsy- stemen Jüngere Entwicklungen im Bereich der Telekonferenzsysteme scheinen dieser Technik nach bisher mangelnder kommerzieller Akzeptanz doch noch zum Durchbruch zu verhelfen. Dabei sind besonders die Tendenzen zur Unterstützung von Mehrpunkt- und Multimediakommunika- tion, zur Realisierung von Produkten auf der Basis internationaler Standards und zur Nutzung weitverbreiteter Telekommunikationsnetze hervorzuheben. Die wohl größte Bedeutung kommt jedoch der nahtlosen Integration der Telekonferenztechnik in den Arbeitsplatzrechner zu, die zur Entstehung von Desktop-Multimedia-Konferenzsystemen (DMC-Systemen) geführt hat. Gegenüber dem intensiv bearbeiteten Gebiet der Echtzeitkommunikation ist die Unterstützung für in Telekonferenzen zu integrierende Anwendungskooperation und die dafür erforderliche Daten- oder Nicht-Echtzeit-Kommunikation vergleichsweise unterentwickelt. Gerade der Datenaustausch zwischen verteilten Anwendungssystemen im Rahmen einer Multimedia-Telekonferenz ist jedoch für viele Kooperationsszenarien von grundlegender Bedeutung, etwa zur gemeinsamen Bear- beitung eines Textes oder als Visualisierungshilfe in Diskussionen. Die vorliegende Arbeit entstand im Kontext des EURO.VISION-Projekts, das die Entwicklung eines DMC-Systems inklusive einer Entwicklungsplattform für Telekonferenzanwendungen zum Ziel hat. Gegenstand dieser Arbeit ist die Entwicklung einer Infrastruktur für Mehrpunkt- Datenkommunikation in Telekonferenzen — Multipoint Communication Layer (MCL) —, die in das EURO.VISION-System eingebettet ist und die Integration verteilter Anwendungssysteme ermöglicht. Das MCL-Konzept beschreibt eine auf die speziellen Anforderungen der Anwen- dungskooperation in Telekonferenzen zugeschnittene Architektur, die aus einer umfassenden Betrachtung der Kooperationsvorgänge in (Tele-)Konferenzen heraus entwickelt wurde und sowohl reine Gruppenkommunikationsdienste bereitstellt, als auch an verschiedene Konferenz- szenarien anpaßbare Konferenzsteuerungsfunktionalität umfaßt. Wegen der zentralen Bedeutung der internationalen Standardisierung für die globale Entwicklung der Telekommunikationstechnik hat während der Entwicklung des MCL-Konzepts eine enge Zusammenarbeit mit den relevanten Standardisierungsgremien stattgefunden. So wird insbesondere die T.120-Serie von ITU-T-Empfehlungen als Basis für die Implementierung des MCL-Konzepts verwendet, gleich- zeitig wurde aber auch signifikant zu deren Weiterentwicklung beigetragen. Abstract Ott, Jörg: A Multipoint Data Communication Infrastructure for Standards-based Teleconferencing Systems More recent developments in the area of teleconferencing systems seem to finally promote this technology’s breakthrough after the past lack of widespread commercial acceptance. In particu- lar, trends towards support of multipoint and multimedia communications, towards implementa- tion of products based upon international standards, and towards utilization of widely available communication networks are to be emphasized. The probably largest importance, however, is attached to the seamless integration of teleconferencing technology with the personal workstation leading to the emergence of Desktop Multimedia Conferencing systems (DMC systems). In contrast to the well advanced research area of real-time communications, support for applica- tions for collaboration as integrated part of teleconferencing systems and the data or non-real- time communication required for those types of applications are far less developed. However, it is specifically the data exchange between distributed application system entities in the context of a multimedia conference that is of crucial importance to many teleconferencing scenarios, e. g. for joint editing of a text or as visualization aid in discussions. The present thesis evolved in the context of the EURO.VISION project which aims at the devel- opment of a DMC system including a development platform for teleconferencing applications. The subject of this thesis is the development of an infrastructure for multipoint data communica- tion in teleconferences — Multipoint Communication Layer (MCL) — that is embedded in the EURO.VISION system and that enables the integration of distributed application systems. The MCL concept defines an architecture that is specifically tailored to the needs of cooperating appli- cations in teleconferences. The MCL was developed based upon a comprehensive review of cooperation processes in (tele-)conferences and provides group communication services as well as conference control services adaptable to different conferencing scenarios. Because of the out- standing importance of international standardization for the global development of telecommuni- cation technology, a close collaboration with the relevant standardization bodies took place during the entire development of the MCL concept. In particular, the T.120 series of ITU-T Recommen- dations was taken as a basis for the implementation of the MCL concept and, in parallel, the fur- ther development of T.120 was significantly influenced by the author. Acknowledgments This thesis reflects the results of the research I have carried out from 1992 to 1997 at the Tech- nische Universität Berlin in the Communications and Operating Systems Research Group created by Prof. Dr.-Ing. Sigram Schindler. An undertaking like this thesis is, of course, accompanied by frequent interactions — discussions, idea exchanges, and so forth — with many others, who thereby have contributed to this thesis as a whole. I would like to take this opportunity to thank all those who have supported me in this effort. First and foremost, I would like to express my highest appreciation for the contributions of Prof. Dr.-Ing. Sigram Schindler to this thesis. It was his visionary engagement in the research area of multimedia teleconferencing in the late 1980s that gav eme the opportunity to participate in research about and the development of various prototypes of teleconferencing systems, starting in 1990 — at a time when I still was a student of computer science at the TU Berlin. He did not only provide organizational and technical foundations for the past five years of intense research and development; I particularly appreciate the many conceptual discussions we had over the years: about the system architecture of EURO.VISION, strategies for application sharing, scenar- ios for integrating teleconferencing and telephony, to name just a few. Furthermore, he has early recognized the importance of international standardization for any research and development efforts in the area of telecommunications including teleconferencing. He enabled my regular par- ticipation in the most important standardization bodies for the area of teleconferencing systems (the ITU-T and the IETF), which are the only places where research results can impact the devel- opment of widely accepted communication technology at all. Finally, the early design and imple- mentation experience in this field, running the EURO.VISION project in 1991 and early 1992, and the demanding conceptual work in this context, together with the involvement in international standardization were an unparalleled experience for me I would never want to miss — and which I probably would not have been able to obtain anywhere else. Furthermore, I would like to thank Prof. Dr.-Ing. Ute Bormann and Dr.-Ing. Carsten Bormann for the last five years of very fruitful collaboration in virtually any sort of activities related to telecon- ferencing and (multipoint) communications. The countless hours we have spent together in dis- cussions of concepts, writing papers and standardization contributions, preparing presentations, and attending a total of seven IETF meetings have significantly contributed to all my research efforts. Finally, with respect to my teaching at TU Berlin, I would like to thank Ute for the ISIS script and both of them for approximately one thousand(!) transparencies for ISIS and other lec- tures as well as their virtually permanent availability for any kind of questions I might have had. All of this has facilitated the work a lot and has allowed me to get, easier than expected, into Acknowledgments i teaching our introductory lecture on international standards and telecommunication