General Information on Multicasting

IP Multicasting is a means of sending voice and video data to multiple recipients over a network. Recipients can simply "tune-in" to the IP multicast address. A multicast data packet can reach many recipients at the same time, which is more efficient and causes less network traffic. Note that multicasting refers to sending data to a select group on the network while broadcasting refers to sending data to everyone on the network. A particular IP Multicast address specifies a group of hosts on the network. When data is sent to the IP Multicast group address, the network will deliver the data only to the hosts that are part of this group and to no other hosts. The original data is sent once, and routers along the path to each host send the packet to the appropriate destination.

The Multicast Backbone (MBone) is a global interconnected network of IP multicast capable networks. The MBone facilitates "real-time" communications (i.e. video and voice data) over wide area networks. With MBone, a single packet can have multiple destinations and isn't split up until the last possible moment. This means that it can pass through several routers before it needs to be divided to reach its final destinations. This leads to much more efficient transmission without congestion and also ensures that packets reach multiple destinations at roughly the same time.

Video multicasting is a one-way communication. Recipients cannot transmit back to the sender (as in videoconferencing). Rather, video multicasting is a way for presentations or meetings to be "broadcast" live over a network (e.g. the Internet) to a select group of people who may be quite a distance from the actual event. The live multicast is sent over the network by the means of a streaming program.

To view Multicasts at NCI-Frederick, you must have the appropriate software installed on your system. For more information, please see MBone Access.

If you are interested in learning more about IP Multicasting, check out these external references: (links will open in a new window)

• The Internet Multicast Backbone
• Multicast Backbone FAQ
• IP Multicast Initiative