 illustrating either side of the coin, are detailed in the following. 6.4.1 A Simple, Distributed Point-to-Point Model Peer-to-peer conferencing systems for moderate membership face the grand challenge of remaining robust with respect to the infrastructure. The role a user agent is able to attain in a distributed scenario needs to be adaptively determined according to the constraints of its device and current network attachment. In a simplified scenario, clients may be divided into two groups, distinguished by their ability or inability to act as a focus. A focus must hold a GRUU and have access to necessary processing and network resources. This elementary adaptation scheme can be based on individual decisions of user agents and gives rise to a hybrid architecture of super peers, chosen from potential focus nodes, and remaining leaf nodes. Leaf nodes attach to super peers in subordinate position, whereas potential focus nodes may be assigned to be super peers or leaves. Super peers provide global connectivity among each other and NAT traversal assistance to leaves! while leaf nodes experience super peers in different roles: A leaf nodes sees its next hop super peer as the conference focus, while the remote super peers act as proxies on the path to any leave located behind them. This set-up corresponds to the well-known architecture of Gnutella 0.6 and successive hybrid unstructured peer-to-peer systems, see [43]. Despite its architectural analogy, a routing layer for real-time group applications should follow a different design. Il Super peers are globally addressable nodes with packet relaying function. TURN will be the natural unilateral self-address fixing (UNSAF) protocol to use. *This architecture relies on the presence of at least one globally addressable, sufficiently powerful peer. In scenarios, where this is likely to fail, a common practice of vendors or communities is to permanently deploy a "silent" relay-peer at some unrestricted place. C 2009 by Taylor & Francis Group, LLC Group Conference Manageme