Also known as: IGMP, IGMP snooping
Without multicast, every TV set gets its own copy of the same channel. With a hundred rooms watching the same news broadcast, that's the same data sent a hundred times through the same switch.
With multicast, the source sends a single stream and the switches only branch it at the last point. IGMP snooping ensures a stream is only forwarded on ports where someone is actually watching.
If multicast isn't configured properly, you get either a stuttering picture or TV traffic that floods the whole network and slows down the wifi too.
How we apply this
On every IPTV installation we configure multicast and IGMP snooping on the switches, so TV and data traffic don't get in each other's way.