iations have been part of the initial arrival steps for each party. Media distribution will naturally follow the paths of the estab- lished routing topology, where super peers can act as two-sided mixers: They may combine media streams arriving from their attached leaf nodes before peering them within the focus mesh, but may as well mix media arriving from neighboring super peers for a lean transmission to leaves. 6.4.2 Scalable, Peer-Centric Conferencing Based on SSM In the presence of source-specific multicast at the network layer (see Sec- tion 6.2.3), peer-to-peer conferences can scale to very large numbers. Com- plying with the fully distributed ad-hoc paradigm, the following scenario is considered throughout this section. Some party will initiate a conference by contacting one or several peers via unicast addresses as resolved from a SIP URI. Following an initial contact, sig- naling will then be turned to scalable multicast group communication. Later on new parties will join the conference by either calling or being called by an existing member. Such group conference initiation scheme is currently not covered by a SIP standard, nor is the employment of source-specific multicast for group signaling. In order to enable SSM, all dialogs must carefully provi- sion addresses of newly arriving senders to all current group members, which ttA corresponding client protocol extension has not been specified yet, cf. [3]. © 2009 by Taylor & Francis Group, LLC Group Conference Management with SIP need to adapt source specific subscriptions appropriately; see [30] for further details. Central to the approach introduced here is the concept of a fully delocalized focus. Conference signaling and management is entirely delegated to the peers participating in the multicast group. This scheme may be equally applied to an undistinguished group of equal participants or to super peers in a hybrid topology as outlined in the previous section. Hybrid architectures may account for SSM accessibility and shield multicast or conferenc