ditional messages are treated as irrelevant iterates. Note that multicast responses require the requestor to sub- scribe to the same group, and prevent routing of multicast requests via SIP proxy servers. Thus, by pure SIP means, a caller cannot issue an INVITE to a remotely located user group, e.g., route to *@dog net, without having established a global multicast connectivity. § Suitable for large, loosely coupled and mutually unknown parties, this simple scheme only operates through the use of any source multicast and does not allow for dynamic SDP negotiations. ASM media distribution is easily achieved for homogeneous conference members with uniformly matching session descriptions. Such media parame- ter settings may be preappointed out of band or learned from a SAP online announcement. However, SAP is rarely used. Once established, the ASM dis- tribution tree serves as a transparent connectivity layer, delivering all media streams to all parties. 6.2.3.2 Source-Specific Multicast Source-specific multicast (SSM) [28,29], recently released as an initial standard, is considered a promising improvement of group distribution techniques. In contrast to ASM, optimal (S,G) multicast source-rooted trees are constructed immediately from source-specific, i.e., (S,G) subscriptions at the client side, Such a scenario could only be realized by tunneling the multicast SIP request into the destination domain. © 2009 by Taylor & Francis Group, LLC Group Conference Management with SIP without utilizing network flooding or rendezvous points. ASM and SSM can be distinguished from a partitioning of the multicast address space. T It is widely believed that simpler and more selective mechanisms for group distribution in SSM will globally disseminate to many users of multicast infrastructure and services. While any source multicast accounts for easy common address- ing, SSM presupposes source-specific subscriptions. Hence, its use requires a dedicated distribution of source addresses for newly joining session mem- bers, which other