ms alternative schemes in forwarding effi- ciency and robustness, while scaling well up to a hundred nodes, provided a significant fraction of unrestricted, high-performance super peers is available. In addition, this scenario will be bound to low complexity, since no routing intelligence beyond standard SIP logic of next-hop proxying is required. Full mesh topologies are thus considered here as the favorable approach to mid-size multi-party conversations. To explore the corresponding conference scenario in detail, consider an ad-hoc join. A client submits an INVITE to any party. It thereby needs to C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security indicate its potential roles in some way. tt The callee may be a conference focus or leaf node. In the first case, it will be aware of the overall leaf node distri- bution from the conference event states and will transfer the newly joining party to the least-occupied super peer by a REFER, e.g., REFER sips: lucy@psychic.org SIP/2.0 CSeq: 9380 REFER Refer-To:<sips:hypnotic-talks@vain-focus.circles.com> Content-Length: 0 In the second situation, the contacted leaf node will issue a re-INVITE to attach the new conference member to its focus, which in turn may refer the caller to another focus for the sake of load balancing. Having indicated its ability to serve as a super peer, the newly arrived party may be selected to join the group of focus nodes. This decision is taken by its current super peer and realized via a third party invite issued to the group of all established focus nodes. The elected super peer will thereby establish point-to-point signaling relationships with all correspondents, leading to an immediate formation of the full mesh conference topology. Focus election and leaf node distribution may be conducted in an individual or collective way, following an eager or lazy strategy. Its implementation most likely will depend on the overall envi- ronment and the conference persistence of super peers. Note that media negot