 minimally offered are authen- ticated and authorized session establishments, including media negotiations. In the presence of media mixers, it uses its session states and the media policy to appropriately configure one or several mixers. For this purpose, the focus interacts with the mixer either through a local interface or, in a distributed scenario, via INVITE/re-INVITE sequences allowing for third party call con- trol (3pcc) [20]. It thereby is fully enabled to (re-)organize media streams at its convenience, e.g., to optimize media distribution according to network and device capabilities. It may follow an efficient strategy of balancing (cascaded) mixers. Additional convenience functions offered by the conference focus most likely are a third party invite (dial-out) for conference-unaware user agents, removal of third parties from the conference, and notification services for con- ference event states. Extended services may be equally included, such as floor control, conference announcements and recordings, Network Address Trans- lation (NAT) traversal assistance, user directory, integration and billing func- tions, etc. 6.2.1.3 Full Distribution The fully distributed multi-party model is built upon peer-to-peer signaling relationships between conference members in the sense that: Participants have the means to contact each other on an individual basis and negotiate SDP; likewise they may inquire on their presence; There is no central point of control nor individual instance of a focus; Some distributed algorithm is cooperatively performed to achieve appro- priate conference coordination and media control. Distributed peer-to-peer management allows for infrastructureless, instanta- neous conference establishment and operation and, if properly designed, may encounter faster and error-resilient dialog handling. In contrast to tight cou- pling, definitions for this conference model are not widely matured, but remain an active area of research and future protocol development. Most simplistically, such a model c