tailieunhanh - The Illustrated Network- P12

The Illustrated Network- P12: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 3 Network Link Technologies 79 On the network end of the DSL link the link terminates at a DSL access multiplexer DSLAM typically using IP or ATM technology. At the user end of the DSL link on the Illustrated Network the office in the home uses both a wired and a wireless network. This is a common arrangement today People with laptops can wander but desktop PCs usually stay put. The wireless network encapsulates packets and sends them to a special device in the home a wireless access point often built into a DSL router . What kind of frames does the DSL link use That s hard to determine because the DSL modem is upstream of the DSL router in most cases sometimes on the side of the house sometimes closer to the service provider . The wired LAN between DSL router and computer uses the same type of Ethernet frames we saw on LAN1 and LAN2. On a wired LAN Ethereal will always capture Ethernet II frames as shown in Figure . What can we learn about DSL itself Well we can access the DSL router using a Web browser and see what kinds of information are available. Figure shows the basic setup screen of the Linksys DSL router although it s really not doing any real routing just functioning as a simple gateway between ISP and home LAN . Because this is a working LAN I ve restored the default names and addresses for this example. The router itself is WRT54G a product designation and the ISP does not expect only one host to use the DSL link so no host or domain name is required. We ll talk about the maximum transmission unit MTU size later in this chapter. This is set automatically on the link. The DSL router itself uses IPv4 address . We ll talk about what the subnet mask does in Chapter 4. The router hands out IP addresses as needed to devices on the home network starting with and it uses the Dynamic Host Configuration Protocol DHCP to do this. We ll talk about DHCP in Chapter 18. - Ethereal 0 He View Qo Qi we