n data format (PIDF). In RFC 4480. Internet Engineering Task Force, July. [15] Lonnfors, M., E. Leppanen, H. Khartabil, and J. Urpalaninen. 2007. Presence information data format (PIDF) extension for partial pres- ence. draft-ietf-simple-partial-pidf-format-10 Internet Engineering Task Force, November. [16] Schulzrinne, H. 2006. Timed presence extensions to the presence infor- mation data format (PIDF) to indicate presence information for past and future time intervals. In RFC 448. Internet Engineering Task Force, July. [17] Peterson, J. 2005. A presence-based GEOPRIV location object format. In RFC 4119. Internet Engineering Task Force, December. © 2009 by Taylor & Francis Group, LLC Group Conference Management with SIP Thomas C. Schmidt and Matthias Wählisch Hamburg University of Applied Sciences CONTENTS 6.1 Introduction Group Conferencing Concepts and Technologies Infrastructure-Assisted Conferences Peer-Managed Conferences Summary and Conclusions References 6.1 Introduction Voice and video conferencing on the Internet is about to become a lightweight day-to-day application. This trend follows from high-bandwidth data con- nections, which are increasingly available to the public at reasonable prices. There is also some remarkable progress in video/audio compression algo- rithms, which reduce a media data stream considerably and reconstruct it again to a high-quality playout sequence on the receiver site. Furthermore, battery powered mobile devices rapidly gain processing and communication performance. They currently can host desktop conferencing software, thereby seamlessly using any Internet connectivity available. Conferencing through the International Telecommunication Union telephone architecture has been known for years as a feature-rich centralized service, suf- fering from its static, complex, and expensive nature. Many of the issues in multi-party communication can be solved in a simpler, more generic way over the Internet, where users, groups, and devices can be addressed individually and independent 