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The Illustrated Network- P45

The Illustrated Network- P45:In this chapter, you will learn about the protocol stack used on the global public Internet and how these protocols have been evolving in today’s world. We’ll review some key basic defi nitions and see the network used to illustrate all of the examples in this book, as well as the packet content, the role that hosts and routers play on the network, and how graphic user and command line interfaces (GUI and CLI, respectively) both are used to interact with devices. | CHAPTER 16 Multicast 409 Uninterested Host Interested Host Group A Uninterested Host Interested Host Group B Interested Interested Host Host Group B Group B FIGURE 16.3 Examples of multicast terminology showing how multicast trees are rooted at the source. JOINs are also sent using IGMP from receivers to local routers. check . Figure 16.3 shows a general view of some of the terms commonly used in an IP multicast network. The key component of the multicast network is the multicast-capable router which replicates the packets. The routers in the IP multicast network which has exactly the same topology as the unicast network it is based on use a multicast routing protocol to build a distribution tree to connect receivers this term is preferred to the multimedia implications of listeners but the listener term is also used to sources. The distribution tree is rooted at the source. The interface on the router leading toward the source is the upstream interface although the less precise terms incoming or inbound interface are also used. There should be only one upstream interface on the router receiving multicast packets. The interface on the router leading toward the receivers is the downstream interface although the less precise terms outgoing or outbound interface are used as well. There can be 0 to N - 1 downstream interfaces on a router where N is the number of logical interfaces on the router. To prevent looping the upstream interface should never receive copies of downstream multicast packets. Routing loops are disastrous in multicast networks because of the repeated replication of packets. Modern multicast routing protocols need to avoid routing loops packet by packet much more rigorously than in unicast routing protocols. Each subnetwork with hosts on the router that has at least one interested receiver is a leaf on the distribution tree. Routers can have multiple leafs or leaves both terms are used on different interfaces and must send a copy of the IP multicast