TABLE OF CONTENTS Multicasting is the process of simultaneously sending a single video signal to multiple users. All viewers get the same signal at the same time, just as in traditional television broadcasting. Virtually all commercial video broadcasting operates using the concept of multicasting including cable TV, satellite TV, and over-the-air TV broadcasting. However, when IP networks are used, multicasting is the exception rather than the rule. In this chapter, we'll look at how multicasting works and then look at a few applications. We'll also investigate the technology of IP multicasting and get an understanding of the impact that multicasting has on a data network.
If you want to understand multicasting, it is helpful to compare it to the process of unicasting. In unicasting, each video stream is sent to exactly one recipient. If multiple recipients want the same video, the source must create a separate unicast stream for each recipient. These streams then flow all the way from the source to each destination over the IP network.
In multicasting, a single video stream is sent simultaneously to multiple users. Through the use of special protocols, the network is directed to make copies of the video stream for every recipient. This process of copying occurs inside the network, rather than at the video source. Copies are made at each point in the network only where they are needed. Figure 9-1 shows the difference in the way data flows under unicasting and multicasting.
Note that IP networks...
