Building resistance to DoS attacks, wherever possible, is another group goal.
Most Internet traffic is unicast, a single source sending to a single destination.
Multicast permits members of a group to communicate with each other by sending and receiving data to and from the group's multicast address. Hosts join multicast groups by notifying multicast-enabled routers that they want to receive packets sent to that group's address. The router joins the group on behalf of the original client and multicast packets are transmitted only to the requesting nodes. Securing unicast traffic isn't easy, even with the years of research and experience backing IPSec. Attackers can spoof a multicast stream and replace a business meeting's video feed with a fake.