In this chapter, we have looked at conference control systems, raning from centralised, through distributed at the application level, as with MCUs in ISDN based systems, on to multicast based ones using a conference control channel or bus as the basic paradigm for messaging between conferencing components. The CCCP protocol was designed to be exemplary. It is probably far to complex to be implemented in its entirity.
For small to medium scale in terms of numbers of participants, the H.320 systems approach is feasible, and can be made to work on packet nets by simulating the circuits for control messages by using a reliable multicast protocol. For larger scale conferences, the Mbone approach, and use of multicast scales to large numbers of senders and receivers, but more work is needed on the protocols and standards to provide tight control of a set of participants.
We will certainly see interworking units relaying between systems employing these two approaches - indeed, H.323 addresses simple dissemination of media from an H.320 type system onto LAN based receivers. It is only a matter of time before systems work the other way too.