In this report, we present measurements of IP multicast traffic taken at the University of California at Berkeley. We note that the volume and distribution of IP multicast traffic is highly variable, and can depend on a small number of active conversations. From examining many-way multimedia conferences, we note the need for some kind of conference control, either provided by the application or the users. We see that IP multicast conferencing traffic can exhibit characteristics very different from that of conventional wide-area data traffic. Finally, we show that scope control (controlling the extent of the propagation of data through the network) must be addressed by the network, because users have been seen to mismanage the scopes of their own transmissions.