Chapter 14. Multicast Protocols

Demand for multimedia, combining audio, video, and data streams over a network, is rapidly increasing. Users are clamoring for it; Web sites are deploying it; businesses and industry see it as a profit center. Some of the more popular uses of multimedia are real-time interactive applications, such as desktop video and audio conferencing, collaborative engineering, shared whiteboards , transmission of training lectures to remote audiences, and animated simulations. Even when data compression is used, multimedia applications require lots of bandwidth.

Enter multicasting, which at its simplest level allows a single transmission to be sent from a server, for example, to multiple receivers. This means that every receiver need not have a unicast transmission with the server. This results in reduced load on the server because it only needs to send the data once and reduced network utilization, leaving expensive WAN bandwidth for other traffic.

Consider the bandwidth utilization chart shown in Figure 14-1. We can see that when unicast transmission is employed to send data, utilization is exponential; however, with multicast it is much more even. This allows for a more manageable and economic use of the available bandwidth. Thus, it is this economic benefit that will continue to drive the adoption of multicast throughout the Internet.

Figure 14-1. Comparison of Unicast and Multicast Bandwidth Utilization

This chapter provides an overview of the more commonly deployed multicast technologies possible on Juniper Networks routers. It will explain them, discuss how they operate , and look at methods for implementing them. While this is a technical discussion and not a sales presentation, the reasons to consider multicast in your network are growing ever stronger and should be considered carefully .

It should also be noted that there are many RFCs dedicated to describing each of the different multicast technologies discussed in this chapter as well as in entire books devoted just to multicast. This chapter does not try to be a complete solution or provide final word on anything multicast; it is an introduction. The goal of this chapter is to introduce you to the world of multicast by opening the door, sharing some perspectives, and demonstrating how multicast is configured on a Juniper Networks router. Some readers will decide they need more information; others will find this chapter's coverage perfect for their needs. For those needing more information, interspersed throughout this chapter are references to additional sources, and readers are encouraged to take advantage of the bibliography as well.