It has been argued that the problem with the Internet model of multimedia conferencing is that it doesn't support simple phone calls, or secure closed ``tightly managed'' conferences.
However, it is easy to add this functionality after one has built a scalable system such as the Mbone provides, rather than limiting the system in the first place. For example, the management of keys can provide a closed group very simply. If one is concerned about traffic analysis, then the use of secure management of IP group address usage would achieve the effect of limiting where multicast traffic propagated. Finally, a telephone style signaling protocol can be provided easily to "launch" the applications using the appropriate keys and addresses, simply by giving the users a nice GUI to a distributed calling protocol system.
Currently, the IETF working group on Conference Control is liasing with the T.120 standards work in the ITU and have made some statements about partial progress.