tailieunhanh - Lecture Business data communications: Chapter 12 - Behrouz A. Forouzan

Chapter 12 - Connecting LANs and WANs: Making backbone networks. In this chapter, we discuss devices that connect LANs and WANs and devices used for connection within a network. Backbone networks, networks that connect other networks, are also a topic of this chapter. | Chapter 12 Connecting LANs and WANs: Making Backbone Networks Differentiate between the different connecting devices and the layers each supports. Understand the functionality of a repeater and where it is used. Understand the difference between a two-layer and a three- layer switch. After reading this chapter, the reader should be able to: OBJECTIVES Understand the functionality of a bridge and where it is used. Understand the functionality of a router and where it is used. OBJECTIVES (continued) Distinguish between a logical bus and logical star backbone. Distinguish between a bridge-based and a router-based back- bone network. Understand the functionality of a backbone network and where it is used. CONNECTING DEVICES Figure 12-1 Connecting devices Figure 12-2 Repeater A repeater connects segments of a LAN together. Note: A repeater forwards every packet; it has no filtering capability. Note: Technical Focus: Repeaters and Amplifiers It is tempting to compare a repeater to an | Chapter 12 Connecting LANs and WANs: Making Backbone Networks Differentiate between the different connecting devices and the layers each supports. Understand the functionality of a repeater and where it is used. Understand the difference between a two-layer and a three- layer switch. After reading this chapter, the reader should be able to: OBJECTIVES Understand the functionality of a bridge and where it is used. Understand the functionality of a router and where it is used. OBJECTIVES (continued) Distinguish between a logical bus and logical star backbone. Distinguish between a bridge-based and a router-based back- bone network. Understand the functionality of a backbone network and where it is used. CONNECTING DEVICES Figure 12-1 Connecting devices Figure 12-2 Repeater A repeater connects segments of a LAN together. Note: A repeater forwards every packet; it has no filtering capability. Note: Technical Focus: Repeaters and Amplifiers It is tempting to compare a repeater to an amplifier, but the comparison is inaccurate. An amplifier cannot discriminate between the intended signal and noise; it amplifies equally everything fed into it. A repeater does not amplify the signal; it regenerates it. When it receives a weakened or corrupted signal, it creates a copy bit for bit, at the original strength. A repeater is a regenerator, not an amplifier. Figure 12-3 Hubs Technical Focus: Active versus Passive Hub A passive hub is a hub that is used to create a connection; it does not regenerate signals. An active hub, on the other hand, is a connector as well as a repeater. Today, most hubs are active hubs. A bridge has a table used in filtering decisions. Note: Figure 12-4 Bridge A bridge connects segments of a LAN together. Note: A router is a three-layer (physical, data link, and network) device. Note: A repeater or a bridge connects segments of LAN together A router connects independent LANs or WANs to create an internetwork (internet). Note: Figure 12-5 Routing