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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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eval('top.frames.main_frame.location.href="'+ContentRef+'referencecontroller_crf.html"'); chapter = "knet-v214aCH47505"; ch_dash = chapter.indexOf('-'); ch_sub1 = chapter.substring(0,ch_dash); ch_sub2 = chapter.substring(ch_dash+1); params = "CHAPID=" + chapter + "/RLOID=" + "knet-v214aRLO47653" + "/RIOID=" + "knet-v214aRIO121174"; returnRef = "../../../../../"+ params + "/"+ ch_sub1 +"/"+ ch_sub2 +"/pageframeset.html"; top.prevPage = returnRef; } function launchFile(filepath) { newWindow = window.open(filepath,"","top=70,left=120,width="+(screen.width*.50)+",height="+(screen.height*.50)+",resizable=yes,scrollbars=yes,toolbar=yes,menubar=yes,status=yes"); /* if (is.ie && filepath.lastIndexOf(".pdf") != -1) { pageTimer = setInterval("winLoadCheck()", 1000); } */ } function winLoadCheck() { if (newWindow.document.readyState == 'complete') { clearInterval(pageTimer); newWindow.location.reload(); } } // BrowserCheck Object // provides most commonly needed browser checking variables // 19990326 // Copyright (C) 1999 Dan Steinman // Distributed under the terms of the GNU Library General Public License // Available at http://www.dansteinman.com/dynapi/ function BrowserCheck() { var b = navigator.appName if (b=="Netscape") this.b = "ns" else if (b=="Microsoft Internet Explorer") this.b = "ie" else this.b = b this.v = parseInt(navigator.appVersion) this.ns = (this.b=="ns" && this.v>=4) this.ns4 = (this.b=="ns" && this.v==4) this.ns5 = (this.b=="ns" && this.v==5) this.ie = (this.b=="ie" && this.v>=4) this.ie4 = (navigator.userAgent.indexOf('MSIE 4')>0) this.ie5 = (navigator.appVersion.indexOf('MSIE 5.0')>0) this.ie55 = (navigator.appVersion.indexOf('MSIE 5.5')>0) if (this.ie5) this.v = 5 this.min = (this.ns||this.ie) } // automatically create the "is" object is = new BrowserCheck()</script> </head> <body onLoad="window.focus();" alink="#000000" vlink="#000000" link="#000000" bgcolor="#E7E7E7" background="../../../../../images/ccna/common/bg.gif"> <table width="100%" cellspacing="0" cellpadding="2" border="0"><tr> <td bgcolor="#000000"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td class="rlohdr"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td valign="top" class="rlohdr">5.2</td><td width="100%" class="rlohdr"> <table width="90%" cellpadding="0" cellspacing="0" border="0"> <tr> <td class="rlohdr">Cable Specification and Termination</td> </tr> </table> </td> </tr> <tr> <td bgcolor="#000000"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td class="riohdr"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td valign="top" class="riohdr">5.2.1</td><td width="100%" class="riohdr"> <table width="90%" cellpadding="0" cellspacing="0" border="0"> <tr> <td class="riohdr">Purpose of LAN media specifications</td> </tr> </table> </td> </tr> <tr> <td colspan="4"> <table width="90%" cellspacing="0" cellpadding="0" border="0"> <tr> <td class="smtext"> <p> </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" cellspacing="0" cellpadding="2" width="100%" border="0"> <tr> <td valign="middle"><img height="22" width="22" border="0" src="../../../../../images/ccna/common/inotes.gif"></td><td valign="middle"><span class="cstitle">Instructor Note</span></td> </tr> <tr> <td valign="top"> </td><td valign="top"><span class="cstext"> <p>The purpose of this target indicator is to underscore the importance of the "alphabet soup" of acronyms that govern networking media standards. It is important to convey that these standards bodies are living, breathing entities. These groups meet regularly to ensure that the commercial diversity of networking product options does not descend into chaos.</p> <p>This TI relates to the Layer 1 part of CCNA Certification Exam Objective #1.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>By the mid 1980s, growing pains from expansion in the field of networking were felt, especially by companies that had instituted many different network technologies. It became increasingly difficult for networks that used different specifications and implementations to communicate with each other. The <i>International Organization for Standardization (ISO)</i> researched various networks and created a network model called the <i>OSI Reference Model</i>. It was designed to help vendors create networks that would work compatibly and interoperably. By creating the OSI model, the ISO provided vendors with a set of standards.</p><table cellpadding="0" cellspacing="0" border="0"> <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="3" border="0"> <tr> <td><span class="note"><b>NOTE:</b><p>Do not confuse the name of the model [OSI] with the name of the organization [ISO].</p></span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>Standards are sets of rules or procedures that are either widely used or officially specified. They serve as a gauge or model of excellence. The OSI model standards ensured compatibility and interoperability between the various types of network technologies that were produced by the many companies around the world. The early standards that were developed for networking media were largely proprietary. They were developed for use by various companies. Many more organizations and government bodies eventually joined the movement to regulate and specify the types of cable that could be used for specific purposes or functions. There has been a confusing mix of standards governing networking media until recently. Standards have ranged from fire and building codes to detailed electrical specifications. Others have focused on tests to ensure safety and performance.</p><p>When designing and building networks, compliance with applicable fire codes, building codes, and safety standards is important. Established performance standards should also be followed in order to ensure optimal network operation. This guarantees compatibility and interoperability in networking media. Standards for networking media have been developed and issued by several groups:</p><ul type="disc"><li> <i>IEEE</i> - Institute of Electrical and Electronics Engineers</li><li> <i>UL</i> - Underwriters Laboratories</li><li> <i>EIA</i> - Electronic Industries Alliance</li><li> <i>TIA</i> - Telecommunications Industry Association</li></ul><p>The latter two organizations issue a list of standards that you will frequently see listed as the <i>TIA/EIA</i> standards. In addition to these groups and organizations, local, state, county, and national government agencies issue specifications and requirements. These requirements can impact the type of cabling that can be used in a local area network.</p><p>The IEEE has outlined cabling requirements in its 802.3 and 802.5 specifications for Ethernet and Token Ring systems. The standards for FDDI were developed by ANSI and ISO/IEC. Underwriters Laboratories issues cabling specifications that are primarily concerned with safety standards. They also rate twisted pair networking media for performance. The Underwriters Laboratories established an identification program that lists markings for shielded and unshielded twisted-pair networking media. This program simplifies the job of ensuring that materials used in LAN installations meet specifications.</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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