Scaling from tightly coupled to loosely coupled conferences

CCCP originates in part as a result of experience gained from centralised Multimedia Conference Control system. centralised system intended for use over ISDN. As described earlier in this chapter, the functionality such systems provided can be summarised up by listing its basic primitives:

• Create conference
• Join/Leave Conference
• List members of conference
• Include/exclude application in conference
• Take floor

In addition, there were a number of asynchronous notification events:

• Floor change
• Participant joining/leaving
• Application included/excluded

The application model was modeled around applications that could replicate either themselves or their display onto remote machines if they were given a list of addresses or displays, hence the include/exclude functionality. However, these are the basic primitives required to support a tightly coupled conference, although for some uses others may be added.

Any conference control system that claims to be fairly generic must be able to support these primitives with reasonable reliability. (Absolute consistency is not really a feasible option in a multiway conference)

Loosely coupled conferences put less constrains on the protocols used, but must scale to much larger numbers, and must be very tolerant of loss and network segmentation.

Taking the modular approach described above, we would expect to change conference controllers when moving from one regime to another, but we do not wish to change the media applications ^7.4 too.