semantics. This opportunity is extensively used for conferencing, resulting in a large number of conceptual documents describing standard extensions, best current practices, draft proposals, etc., see [2] for a guided overview. The present contribution does not enumerate proposed features, but rather concentrates on core concepts and tries to outline con- ferencing solutions of common use as well as future directions of promising development. This chapter will first illustrate the fundamental issues and SIP concepts for multiparty conversations along the line of examples and characteristic appli- cations. An overview of core concepts and technologies for SIP-initiated group conferencing follows in Section 6.2. Point-to-point schemes and multicast solu- tions are covered herein, as well as mobility aspects. Section 6.3 then takes a closer look at SIP standard infrastructure components and their potential to facilitate group conferencing in an uncomplex manner. A detailed discus- sion of conferences solely managed by peers is the focus of the subsequent Section 6.4. Finally, a summary and conclusions will complete this report on conferencing. 6.1.1 Two Introductory Scenarios Group communication can be of manifold nature and a variety of quite differ- ent views or scenarios have been contributed to the field. For a start at a prime perspective, two well-known and established synchronous group communica- tion services from everyday life are considered: The three-way conference, such as Integrated Services Digital Network (ISDN) telephone systems on the one hand, and the reception of live broadcast media such as radio and television, with an optional offer of selective feedback channels, on the other. While in © 2009 by Taylor & Francis Group, LLC Group Conference Management with SIP INVITE re-INVITE Contact Contact sips dog-matter@ sips dog-matter@ [SDP] [SDP] Charlie OK[SDP] OK[SDP] Snoopy FIGURE 6.1 A three-party dialog. the first scenario users act primarily dialog-oriented, most of them are bound to passive recep