How many people can be involved?

There are two aspects to this question. The first is about "number of viewers of a conference" and the second is "number of links to the conference". For example a video conference could be projected on a large screen in a lecture theatre and serve many hundreds of viewers through one link.

The technical limitation to the number of links is normally higher than the practical limit of interaction. For example a group of 40 Trainee Teachers could observe a lesson, but managing each  of them asking questions can be very complicated.

Multipoint conferences (with two or more links to the conference) can easily be run for a dozen participants, however again at this scale ensuring everyone is able to take a full part can be challenging.

A practical limit for multipoint conferences where meaningful interaction is important is between four and six sites.