Multicasting

From the old issue of PCQuest magazine on video streaming;

Using unicast, video contents can be communicated to a single machine on a network—a peer-to-peer communication. For such communication, you need to specify the exact IP address of the target machine.

With broadcast, content is communicated to all the machines on the network. All machines receive the content even if they don’t intend to. Such content is delivered using broadcast address for a network. For example, the broadcast address for a 192.168.1.0 network is 192.168.1.255.

For video streaming, neither unicast nor broadcast may be suitable. You may not want to stream video to only one machine. You may like more than one machine to receive the video stream so that more users can watch the video. If you opt for broadcast, you may end up wasting network bandwidth by streaming heavy content like video to all machines and hence to users who might not be interested in watching the video.

This is where Multicast comes to the rescue. In multicast, the server streams the content to a particular IP in the range of 224.0.0.0 to 239.255.255.255. This IP does not fall in the range of the prescribed IP addresses for computer networks. Hence, content delivered to this IP is not received by any machine on the network. Only when a machine connects to this IP, will it be able to retrieve the content and more than one machine can connect to a multicast IP simultaneously.

Full article can be found here.