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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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Computer applications -- Eudora for email, Netscape Navigator and Internet Explorer as browsers -- are classified "above" the 7 layers of the OSI model. It is only when such programs make network requests and require network services that they are dealing with OSI Layer 7 protocols such as POP3, DNS, http, and ftp. Not everything fits within the OSI model.</p> <p>This TI relates to CCNA Certification Exam Objectives #1.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>You select network applications based on the type of work you need to accomplish. A complete set of application layer programs is available to interface with the Internet. Each application program type is associated with its own application protocol. Although there are more programs and protocol types available, the following are the main focus of this chapter:</p><ul type="disc"><li>The World Wide Web uses the HTTP protocol.<img border="0" src="../../../../../CHAPID=knet-v214aCH47515/RLOID=knet-v214aRLO48009/RIOID=knet-v214aRIO124719/knet/v214adataimage1/1.gif" width="12" height="12"></li><li>Remote access programs use the Telnet protocol for directly connecting to remote resources.<img border="0" src="../../../../../CHAPID=knet-v214aCH47515/RLOID=knet-v214aRLO48009/RIOID=knet-v214aRIO124719/knet/v214adataimage2/2.gif" width="12" height="12"></li><li>E-mail programs support the POP3 application layer protocol for electronic mail.<img border="0" src="../../../../../CHAPID=knet-v214aCH47515/RLOID=knet-v214aRLO48009/RIOID=knet-v214aRIO124719/knet/v214adataimage3/3.gif" width="12" height="12"></li><li>File utility programs use the FTP protocol for copying and moving files between remote sites.<img border="0" src="../../../../../CHAPID=knet-v214aCH47515/RLOID=knet-v214aRLO48009/RIOID=knet-v214aRIO124719/knet/v214adataimage4/4.gif" width="12" height="12"></li><li>Network data gathering and monitoring applications use the SNMP protocol.</li></ul><p>It is important to re-emphasize the fact that the application layer is just another protocol layer in the OSI or TCP/IP models. The programs interface with application layer protocols.</p><p>E-mail client applications (for example, Eudora, Microsoft Mail, Pegasus, and Netscape Mail) work with the POP3 protocol. The same is true with Web browsers. The two most popular Web browsers are Microsoft Internet Explorer and Netscape Communicator. The appearance and operation of these two programs is very different, but they both work with the application layer HTTP protocol.</p><table cellpadding="0" cellspacing="0" width="100%" border="0" xmlns:java="http://xml.apache.org/xslt/java"> <tr> <td width="100%"><img height="10" width="1" border="0" src="../../../../../images/ccna/common/transdot.gif"></td> </tr> <tr> <td width="100%"> <table bgcolor="#000000" bordercolor="#000000" cellspacing="0" bordercolorlight="#000000" width="100%" border="0"> <tr> <td width="100%"> <table bgcolor="#FFFFFF" width="100%" cellspacing="0" cellpadding="0" border="0"> <tr> <td> <table bgcolor="#FFFFFF" cellpadding="2" width="100%" border="0"> <tr> <td valign="top"><img height="22" width="22" border="0" src="../../../../../images/ccna/common/icon10.gif"></td><td valign="middle"><span class="cstitle"><a href="#" onClick="window.open('../../../../../CHAPID=null/RLOID=null/RIOID=knet-v214aRIOv2141009/knet/v214aRIOv2141009/iaactivity.html','LabActivity','width=742,height=390,toolbar=0,scrollbars=0,left=26,top=38');void(null);">Interactive Lab Activity</a></span></td> </tr> <tr> <td valign="top"> </td><td valign="top"><span class="cstext"> <p>Application Layer Software</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table> </td> </tr> </table> <p xmlns:java="http://xml.apache.org/xslt/java"> </p></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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