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Chapter 6. Network Hardware Components (... > End-of-Chapter Commentary - Pg. 236

236 Networking Explained, Second Edition sible by all ports (called shared-memory queuing). Each location strategy has its advan- tages and disadvantages. Finally, some switches also have multiple queues per port, which are needed to address QoS issues (see Chapter 5). As for a switch's implementation model, this refers to the manner in which switching decisions are made. For example, a centralized switch model relies on a central forwarding table that is accessible by all ports, whereas a distributed switching model enables ports to maintain their own lookup tables, which are synchronized with a master address table. 57. I have heard and read about "layer-3 switching" and "layer-3 switches." Frankly, I am a little confused by these concepts. Could you shed some light on this? Sure, but not here. This is discussed in Chapter 7 when we examine the differences between routers and switches. For the moment, though, suffice it to say that Layers 2 and 3 of the OSI model are merging and it is becoming difficult to distinguish between tradi- tional layer-2 devices such as LAN switches and layer-3 devices such as routers. END-OF-CHAPTER COMMENTARY This concludes our discussion of layer 1 and layer 2 network components. In subsequent chapters some of the concepts discussed in this chapter are extended. For example, in Chapter 7, we discuss WANs, internetworking, and network layer (layer 3) concepts and components. Two topics that are discussed in Chapter 7 that were referenced in the current chapter are routers and switches. Another topic of this chapter, Ethernet switches, is expanded on in Chapter 8. The topic of switching is also extended in later chapters. For example, token ring switching is discussed in Chapter 9, FDDI switching is discussed in