multicasting old school.
Multicasting is good for "broadcasting like services" to lots of watchers, eg London traffic cams and Empire State. The multicast enabled routers duplicate on demand. Which makes a bandwidth billing issue. But there are better ways to do this now. A single PC NIC is Gigabit and can feed 1000 whatchers. Netflix, Youtube look at traffic flows and put servers where they need to in your IPS racks. They cache near to customer what they can. They duplicate flows where they need to.
Multicast is still good for CCTV but off the internet.