ccna 2.0

ccna 2.0.15.2.1 Connecting to an Enterprise's Private WANWAN services typically create either a private WAN service or a public WAN service. In the case of a private WAN, a customer connects to a WAN service provider from many locations. This provider ensures that data is forwarded between these sites. Subsequently, when a second customer connects to the same WAN service, the WAN service allows the two customers' data to be independent of each other (private). While data may flow through the same equipment into the provider's network, the provider never forwards data sent by Customer 1 to Customer 2, or vice versa, thus making the network private from the customer's perspective.In contrast, an Internet connection can only be established if each customer of an Internet Service Provider (ISP) is able and willing to send and receive packets from other customers. Adding a connection to the Internet through an ISP indicates that the user is willing to send and receive packets over that connection. To protect that connection, people must be concerned about security and allow only data traffic of the correct data type to flow over their Internet access link.You can use most of the WAN technologies mentioned in this chapter to build both private WANs and the public Internet. however, some technologies may be better suited for one or the other, so this chapter will discuss each WAN technology as it relates to the technology. The first part of this chapter looks at WAN technologies in private WAN services. these WAN technologies specifically include the following: . Leased line Frame RelayEthernet WANMPLSVSATLeased LinesOf all the WAN topics mentioned in this book, leased lines and frame relay are two obvious focuses. Leased lines have already been discussed to some extent in Chapter 12, "Point-to-Point WANs," and they are often used in conjunction with data link protocols. Why are they covered further here in this chapter? It is for comparison with the other WAN technologies in this chapter.One of the ICND2 (and CCNA) exam topics says it all: be prepared to identify a variety of WAN technologies. So what is the best way to identify a leased line when you encounter these technologies on the exam? Here's a brief refresher. First, there are many designations for leased lines, so in some respects you should review what is found in Table 12-2 in Chapter 12. In graphs, they are generally represented by curves that look like lightning bolts. There are also graphs that look more like Figure 15-1,represented by the channel service unit/data service unit (CSU/DSU) that each router requires. Note that this diagram shows an external CSU/DSU.