IP for IM and Presence Leveraging Extensions (SIMPLE), has tied this success to SIP. 6.1.5 SIP and the IMS An alternate approach to SIP conferencing is taken with the ITU-T next gen- eration network (NGN) architecture. Using Internet technologies, 3G mobile operators and wire phone companies are in the process of building next gen- eration telephone services based on the IP Multimedia Subsystem (IMS) or its wireline emulation TISPAN. SIP has been selected as the session signaling protocol as RTP was formerly chosen in H.323 for media transport. How- ever, this provider-centric, network-controlled and application-aware network architecture takes a completely different perspective. The IMS accounts for VoIP/VCoIP, presence, messaging, gaming, etc., ser- vices, which as physical server instances, reside on the application server layer. A likewise centralized server instance at this layer will enable conference man- agement. For integration purposes and ease in billing, all these session-oriented services reside on a common session layer, which aggregates states from SIP message exchanges with application servers. As of 3GPP release 6, Multime- dia Broadcast and Multicast Services (MBMS) are foreseen. Anchored at a regional Gateway GPRS Support Node (GGSN), group communication may thus be used to enhance conference data distribution. This strongly debated, complex architecture provides SIP-initiated group conferencing services within a provider domain. The future will uncover the validity of the IMS business model and reveal whether people are willing to pay for dedicated conferencing services offered by operators or just use applications available from indepen- dent sources. C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security 6.2 Group Conferencing Concepts and Technologies Conferencing enriches the semantic of basic group communication by pro- viding presence or session logic to the application. Conversely, it widens the meaning of dialog-oriented conversation by augmenting sign