What is Multicasting?
Multicasting is the ability to transmit a single stream to multiple subscribers at the same time. Unlike conventional streaming, it does not need one stream per recipient. Instead, there is one stream on any one segment of the network on which there is a subscriber.
Using the same amount of spectrum required for one analog program, multicasting allows broadcast stations to offer several channels of digital programming at the same time. For example, a local TV station elects to send out three DTV programs. The first program offers HDTV shows and sports, while the second offers SD versions of the same programming. Finally, a third program carries continuous local weather information. Your digital TV set-top receiver or integrated TV will automatically find all of these programs for you and identify each with a unique channel number.
In this case, the first program (HDTV) would appear as channel 6-1. The second program would come up as channel 6-2, and the 24/7 weather programming would show up as 6-3.
The digital TV or external set-top receiver knows how many of these TV programs are on each channel by reading the digital program data packets. For a better understanding of how this works, think of the TV channel as a “digital shoebox.”