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15 WAN Introduction CERTIFICATION OBJECTIVES 15.01 Wide Area Networking Overview 15.02 HDLCp 15.03 PPP Two-Minute Drill Q&A Self Test 2 Chapter 15: WAN Introduction he last few chapters introduced you to configuring IP features on your Cisco router. This chapter introduces you to wide area networking (WAN) concepts and some basic point-to-point configurations, including HDLC and PPP. The two chapters following this, Frame Relay and ISDN, focus on packet-switched and dialup connections, respectively. CERTIFICATION OBJECTIVE 15.01 Wide Area Networking Overview Typically, LAN connections are within a company and WAN connections allow you to connect to remote sites. Typically, you don’t own the infrastructure for WAN connections—anothercompany,suchasatelephonecompany,providestheinfrastructure. WAN connections are usually slower than LAN connections. A derivative of WAN solutions is the metropolitan area network (MAN). MANs sometimes use high-speed LAN connections in a small geographic area between different companies, or divisions within a company. MANs are becoming more and more popular in large cities and even provide connections over a LAN medium, such as Ethernet. The most important factor in choosing a WAN service is cost. One of the major factors when choosing a WAN or MAN provider is cost.These connections are billed in multiple ways: flat monthly lease cost, per-packet cost, per-minute cost, and many other methods. On top of this, you have many solutions to choose from to solve your WAN connection problems. In order to choose the right solution, you’ll need to weigh your connection requirements, your traffic patterns, and the cost of the solution. Equipment and Components WANconnectionsaremadeupofmanytypesofequipmentandcomponents.Figure15-1 shows some of these WAN terms. Table 15-1 has a list of the terms and definitions. It is important to remember the WAN terms in Table 15-1. As you may recall from Chapter 2, a DCE terminates a connection between two sites and provides clocking and synchronization for that connection; it connects to a DTE. The DCE category includes equipment such as CSU/DSUs, NT1s, and modems. A DTE is an end-user device, Wide Area Networking Overview 3 FIGURE 15-1 WAN terms such as a router or PC, that connects to the WAN via the DCE equipment. In some circumstances, the function of the DCE might be built into the DTE’s physical interface. For instance, certain Cisco routers can be purchased with built-in NT1s or CSU/DSUs in their WAN interfaces. TABLE 15-1 Term WAN Terms and Definitions Definition CPE (customer premises equipment) Demarcation point Local loop CO (central office) switch Toll network This is your network’s equipment, which includes the DCE (modem, NT1, CSU/DSU) and your DTE (router, access server). This is where the responsibility of the carrier is passed on to you; this could be inside or outside your local facility. Please note that this is a logical boundary, not necessarily a physical boundary. This is the connection from the carrier`s switching equipment to the demarcation point. This is the carrier`s switch within the toll network. This is the carrier`s internal infrastructure for transporting your data. 4 Chapter 15: WAN Introduction Connection Types As mentioned at the beginning of this section, you have two major concerns when choosingaWANsolution:costandthetypeofsolution.TherearemanyWANsolutions tochoosefrom,includingthefollowing:analogmodemsandISDNfordialupconnections, ATM, dedicated point-to-point leased lines (dedicated circuits), DSL, Frame Relay, SMDS, wireless (including cellular, laser microwave, radio, and satellite), and X.25. As you can see from this list, you have a lot of choices. Not all of these solutions will be available in every area, and not every solution is ideal for your needs. Therefore, one of your first tasks is to have a basic understanding of some of these services. Chapter 1 provided a brief overview of some of these services. This chapter covers some of these services briefly, and Chapters 16 and 17 expand on some of the others. Typically, WAN connections fall under one of four categories: Know about the four types of WAN connections: leased lines, circuit-switched connections, packet-switched connections, and cell-switched connections. Leased lines, such as dedicated circuits or connections Circuit-switched connections, such as analog modem and digital ISDN dialup connections Packet-switched connections, such as Frame Relay and X.25 Cell-switched connections, such as ATM and SMDS The following three sections will introduce you to these three connection types. Leased-Line Connections A leased-line connection is basically a dedicated circuit connection between two sites. It simulates a single cable connection between the local and remote sites. Leased lines are best suited when both of these conditions hold: The distance between the two sites is small, making them cost-effective. You have a constant amount of traffic between two sites and need to guarantee bandwidth for certain applications. Even though leased lines can provide guaranteed bandwidth and minimal delay for connections, other available solutions, such as ATM, can provide the same features. The main disadvantage of leased lines is their cost—they are the most expensive WAN solution. Leased lines use synchronous serial connections, with their data rates ranging from 2,400 bps all the way up to 45 Mbps, in what is referred to as a DS3 connection. A Wide Area Networking Overview 5 Remember that leased lines are used for short-distance connections and when you have a constant amount of traffic between sites with a need of guaranteed bandwidth. synchronous serial connection allows you to simultaneously send and receive information without having to wait for any signal from the remote side. Nor does a synchronous connection need to indicate when it is beginning to send something or the end of a transmission. These two things, plus how clocking is done, are the three major differences between synchronous and asynchronous connections—asynchronous connections are typically used for dialup connections, such as modems. If you purchase a leased line, you will need the following equipment: DTE A router with a synchronous serial interface: this provides the data link framing and terminates the WAN connection. DCE A CSU/DSU to terminate the carrier’s leased-line connection: this provides the clocking and synchronization for the connection. Figure 15-2 shows an example of the equipment required for a leased-line connection. The CSU/DSU is responsible for handling the physical layer framing, clocking, and synchronization of the connection. Data link layer protocols that you can use for FIGURE 15-2 Leased line example ... - tailieumienphi.vn
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