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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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Notice that the model is hourglass shaped -- many upper layer protocols at the top and a diversity of lower layer LAN protocols at the bottom, with a narrowing at the transport layer (TCP or UDP) all running IP.</p> <p>This TI relates to CCNA Certification Exam Objectives #35 and #36.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>The diagram shown in the figure is called a protocol graph. It illustrates some of the common protocols that are specified by the TCP/IP reference model. At the application layer, you will see different network tasks you may not recognize, but as a user of the Internet, probably use every day. You will examine all of these during the course of the curriculum. These applications include the following: </p><ul type="disc"><li> <b>FTP</b> - File Transfer Protocol </li><li> <b>HTTP</b> - Hypertext Transfer Protocol </li><li> <b>SMTP</b> - Simple Mail Transfer protocol </li><li> <b>DNS</b> - Domain Name System </li><li> <b>TFTP</b> - Trivial File Transfer Protocol </li></ul><p>The TCP/IP model emphasizes maximum flexibility, at the application layer, for developers of software. The transport layer involves two protocols, transmission control protocol (TCP) and user datagram protocol (UDP). These will be examined in detail later in the CCNA curriculum. The lowest layer, the network access layer, refers to the particular LAN or WAN technology that is being used.</p><p>In the TCP/IP model, regardless of which application requests network services, and regardless of which transport protocol is used, there is only one network protocol - internet protocol, or IP. This is a deliberate design decision.<i> IP</i> serves as a universal protocol that allows any computer, anywhere, to communicate at any time.</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://oac3.hsc.uth.tmc.edu/staff/snewton/tcp-tutorial/">Introduction to the Internet Protocols</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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