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<html> <head> <meta content="en-us" http-equiv="Content-Language"> <meta content="text/html; charset=UTF-8" http-equiv="Content-Type"> <link type="text/css" rel="stylesheet" href="../../../../../css/ccna.css"> <script src="../../../../../js/framesetHelper.js" language="JavaScript"></script><script language="JavaScript"> window.scrollTo(0,0); function newPage(pageID) { alert("COMMING SOON!!\nThis feature is currently in development."); } function launchMoreInfo(oid) { dash = oid.indexOf('-'); sub1 = oid.substring(0,dash); sub2 = oid.substring(dash+1); // this is an URL base on the // system that generated the static // download of the curriculum. httpref = "http://nomar.sdf.cisco.com/servlet/org.cli.delivery.rendering.servlet.MIServlet/Static=true,LMSID=DTUI,Engine=dynamic,Theme=cnamstheme,Style=ccna,Language=en,Version=2,RootID=knet-v214aCV47051/CHAPID=null/RLOID=null/RIOID=null/"; newref = httpref + sub1 +"/"+ sub2 +"/moreinfoframeset.html"; //alert("new newref :\n" + newref); window.open(newref,'MoreInfo','toolbar=no,status=yes,menubar=no,location=no,scrollbars=yes,height=442,width=756,left=20,top=20,resizable=yes') } function launchContentResource(contentID) { top.currentSupport = 0; 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Topology refers to the physical and logical diagrams that summarize network connections and information flow. A teaching topology is introduced, which has all of the first semester LAN devices and technologies on it. The ability to read these diagrams is a learned skill. Use the teaching topology to challenge the students: "by the end of this chapter you will be able to read and understand this diagram".</p> <p>This TI relates to CCNA Certification Exam Objective #46.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p> <i>Topology</i> defines the structure of the network. There are two parts to the topology definition: the physical topology, which is the actual layout of the wire (media), and the logical topology, which defines how data flows through the network. Physical topologies commonly used are the Bus, Ring, Star, Extended Star, Hierarchical, and Mesh. These are shown in Figure 1.mediaobject-ref refid="v214adatamedia1"/></p><ul type="disc"><li>A bus topology uses a single backbone segment (length of cable). All the hosts connect to it directly.</li><li>A ring topology connects one host to the next and the last host to the first. This creates a physical ring of cable.</li><li>A star topology connects all cables to a central point. This point is usually a hub or switch.</li><li>An extended star topology links individual stars together by linking the hubs/switches. This will extend the length and size of the network.</li><li>A hierarchical topology is created similar to an extended star. Instead of linking the hubs/switches together, the system is linked to a computer. The computer controls the traffic on the topology.</li><li>A mesh topology is used when there can be absolutely no break in communications. The control systems of a nuclear power plant are a good example. As you can see in Figure [2], each host is connected to all other hosts. This also reflects the design of the Internet, which has multiple paths to any one location.</li></ul><p>The logical topology of a network is how the hosts communicate across the medium. The two most common types of logical topologies are broadcast and token passing. Logical topology also defines the path that information takes through a network. For example, all forms of Ethernet use a logical bus, even when the network is physically wired as a star or extended star. Token Ring networks use a logical ring, because information flows from one host to the next in a predetermined pattern, but in most cases they use a physical star topology.</p><p>Broadcast topology simply means that each host sends its data to all other hosts on the network medium. There is no order the stations follow to use the network, it is first come, first serve. This is the way that Ethernet works and you will learn much more about this later in the semester.</p><p>The second type is token passing. Token-passing controls network access by passing an electronic token sequentially to each host. When a host receives the token, it means that the host can send data on the network. If the host has no data to send, it passes the token to the next host and the process repeats itself.</p><p>The diagram in the figure shows many topologies. <img border="0" src="../../../../../CHAPID=knet-v214aCH47503/RLOID=knet-v214aRLO47534/RIOID=knet-v214aRIO121102/knet/v214adataimage2/2.gif" width="12" height="12"> It shows a LAN of moderate complexity that is typical of a school or a small business. It has many symbols, and depicts many networking concepts. This LAN is typical of a small campus. It represents most of the devices that you will study for your CCNA.</p><table cellpadding="0" cellspacing="4" width="63%" border="0" xmlns:java="http://xml.apache.org/xslt/java"> <tr> <td valign="middle" width="8%"><img height="23" width="23" src="../../../../../images/ccna/common/icon2.gif"></td><td valign="middle" width="92%"><span class="cstitle">Web Links</span></td> </tr> <tr> <td valign="middle" width="8%"> </td><td valign="middle" width="92%"><span class="smtext"><a target="_blank" href="http://webopedia.internet.com/Networks/Network_Topologies/">Webopedia</a></span></td> </tr> </table></td> </tr> </table> </td> </tr></table> <p> </p> <table width="100%" cellspacing="0" cellpadding="2" border="0" valign="bottom"> <tr> <td></td> </tr> </table> </body></html>⌨️ 快捷键说明
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