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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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First, to analyze the flow of materials and ideas in terms of layers. This will help deepen the analogies introduced earlier in the course and help make plausible the idea that communication can be analyzed in layers.</p> <p>Secondly, this target indicator specifically addresses analyzing a human conversation -- as an analogy to computer data communication -- in terms of layers.</p> <p>One activity that works well here is called "At the Drive-Through". Using two walkie-talkies and two bilingual students at different ends of the room, have them simulate the drive-through ordering process. One student plays the role of the customer and the other the restaurant employee. First have the student violate the idea layer protocol by ordering chicken at a hamburger restaurant, or hamburgers at a taco restaurant, and so on. Then have the student violate the representation layer protocol by ordering in a different language. Third, have the student violate the transport layer protocol by not waiting to have their order repeated back to them and speaking too quickly. Finally have the student violate the physical layer protocol by talking and not using the Walkie talkies (short-distance FM radios). Two points should be made: one, communication can be analyzed in layers; two, the layers between the two communicating entities must match. Variations on this theme specific to other cultures are encouraged.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>The concept of <i>layers</i> will help you understand the action that occurs during communication from one computer to another. Shown in the Figure <img border="0" src="../../../../../CHAPID=knet-v214aCH47502/RLOID=knet-v214aRLO47527/RIOID=knet-v214aRIO120881/knet/v214adataimage1/1.gif" width="12" height="12"> are questions that involve the movement of physical objects such as highway traffic, or electronic data. This motion of objects, whether it is physical or logical, is referred to as flow. There are many layers that help describe the details of the flow process. Other examples of systems that flow are the public water system, the highway system, the postal system, and the telephone system.</p><p>Now examine the Figure <img border="0" src="../../../../../CHAPID=knet-v214aCH47502/RLOID=knet-v214aRLO47527/RIOID=knet-v214aRIO120881/knet/v214adataimage2/2.gif" width="12" height="12"> "Comparing Networks" chart. What network are you examining? What is flowing? What are the different forms of the object that is flowing? What are the rules for flow? Where does the flow occur? The networks listed in this chart give you more analogies to help you understand computer networks.</p><p>Another example of how you might use the concept of layers to analyze an everyday subject is to examine human conversation. When you create an idea that you wish to communicate to another person, the first thing you do is choose how you want to express that idea, then you decide how to properly communicate it, and finally, you actually deliver the idea.</p><p>Imagine a young boy seated at one end of a very long dinner table. On the other end of the table, quite a distance away, sits the young boy's grandmother. The youngster speaks English. The grandmother prefers to speak Spanish. The table has been set with a wonderful meal that the grandmother has prepared. Suddenly the young boy shouts at the top of his lungs, "Hey, you! Give me the rice!" and reaches across the table to grab it. In most places, this action is considered quite rude. What should the young boy have done to communicate his wishes in an acceptable manner?</p><p>To help you find the solution to this question, analyze the communication process by using layers. First there is the idea -- the young boy wants rice; then there is the representation of the idea--- spoken English (instead of Spanish); next is the method of delivery -- "Hey, you"; and finally, the medium -- shouting (sound) and grabbing (physical action) across the table for the rice.</p><p>From this group of four layers, you can see that three of them prevent the young boy from communicating his idea in an appropriate/acceptable manner. The first layer (the idea) is acceptable. The second layer (representation), using spoken English instead of Spanish, and the third layer (delivery), demanding instead of a politely requesting, most definitely do not follow acceptable social protocol. The fourth layer (medium), shouting and grabbing from the table rather than politely requesting assistance from another person seated nearby, is unacceptable behavior in most any social situation.</p><p>By analyzing this interaction in terms of layers you can understand more clearly some of the problems of communication in both humans or computers, and how you might solve them.</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://www.rad.com/networks/1994/osi/osi.htm">The OSI Reference Model</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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