What is multicasting?
When a radio station broadcasts in HD, the analog FM signal you have always listened to remains exactly the same. The advantage of this new digital technology is that it allows KJZZ to “multicast.” That is, we can offer two or more additional programming services on a single frequency. These program offerings are “hidden” on standard radios. An HD digital radio receiver allows you to pick up these “hidden” services. NPR’s Jim Zarolli recently reported on HD Radio.
Multicasting is a technique developed to send packets from one location in the Internet to many other locations, without any unnecessary packet duplication. In multicasting, one packet is sent from a source and is replicated as needed in the network to reach as many end-users as necessary. The concept of a group is crucial to multicasting. Every multicast requires a multicast group; the sender (or source) transmits to the group address, and only members of the group can receive the multicast data. A group is defined by a Class D address. Multicasting is not the same as broadcasting on the Internet or on a LAN. In networking jargon, broadcast data are sent to every possible receiver, while multicast packets are sent only to receivers that want them.
• When not transmitting in HDTV, broadcasters will be able to transmit four or more channels of SDTV programming simultaneously. This is called multicasting. Although SDTV will not match HDTV in quality, it will still offer a higher quality picture than NTSC analog versions. When transmitting in HDTV, fewer SD channels will can be multicast at the same time.
