t within the subnet it newly attached to. Agent-based solutions attempt to balance between the previous two mech- anisms. Static agents typically act as local tunneling proxies, allowing for some inter-agent handover, while the mobile node moves away. Work on standardizing seamless solutions has just begun; the requirements are being discussed in the MobOpts research group. For further details and a brief survey on current solutions, we refer to [40]. C 2009 by Taylor & Francis Group, LLC Group Conference Management with SIP Infrastructure-Assisted Conferences Conventional deployments of SIP architectures are accomplished with the help of infrastructural entities, typically a SIP proxy server and registrar, a gate- way, and additional convenience functions. These components typically reside on network nodes that are well connected and in unrestricted, permanent availability. A manifest strategy to advance service offers lies in augmenting these nodes with lightweight side primitives such as NAT traversal assistance or client mobility management. Likewise, a conference control function could reside on a standard SIP server instance. However, media mixing and relay- ing for large conferences cannot be considered lightweight, but out of range. Multicast distribution can assist in serverless delivery of media streams as discussed in Section 6.2.3, and open the floodgates to scalable conferencing at no additonal cost. Unfortunately, IP multicast is not uniformly available, even though all major router vendors and operating systems offer a wide variety of imple- mentations to support it. While many (walled) domains or enterprise net- works operate multicast, group service rollout has been largely limited in public inter-domain scenarios. Application layer multicast based on structured peer-to-peer systems offer group communication in an infrastructure-agnostic fashion. DHT are reasonably efficient and scale over a wide range of group sizes. However, they do not allow for layer two interactions, thus do not facili- tate