Multicast is a multiplier. it gives leverage to senders, but without their knowledge. Multicast (and its application level cousin, the CU-SeeMe reflector)3.7 can ``attract'' more traffic to a site that it can cope with on its Internet access link. A user can do this by inadvertently joining a group for which there is a high-bandwidth sender, and then ``going for a cup of tea''. This problem will be averted through access control, or through mechanisms such as charging which may result from the deployment of real time traffic support as described in chapter 2.