 for the IP media server used in our experiments supports up to a hundred clients. Even though our laboratory testbed uses a much smaller user pool, typically about four, there is no reason not to assume that the signaling protocol can keep up with practical realtime demands and support the same number of session participants. 14.5 Conclusion and Future Research The Media Server Component Model architecture can be deployed for policy- based media-mixing and narrowcasting within the standard SIP framework for multimedia conferencing systems. Narrowcasting privacy command interpre- tation includes a policy evaluation algorithm, a media mixing and delivery mechanism that considers fine-grained policy configured by participants. The policy can be displayed and controlled via interfaces in which hands and other attributes (megaphones and ears trumpets) clapped over figurative avatars' mouths and ears represent audio stream filters. Applications like "Second Life" and virtual environments represent a fertile platform for conferences, distance learning, meetings, and recreational activity like chatspaces. 14.5.1 Practical Conferencing In ordinary conversation, participants generally observe turn-taking, as in a CSMA/CD (carrier sense multiple access/collision detection) protocol with discretionary backup. That is, an utterance that collides with another will cause one or both of the simultaneous speakers to stop and wait until a break before repeating. One might wonder what happens to such conversational turn-taking in the presence of asymmetric media filters and the absence of a moderator. Narrowcasting features-like blocklists, side channels, and call-within-a- call-complicate teleconferences, since a deafened conversant might not be aware that another is talking and multiple sources might speak at once. If some participants in a conference are muted or deafened to some other partic- ipants, without formal floor control there is a likelihood of some "talking on top of" others. In the absence of common floor control, w