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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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Unlike the prior example for choosing a wiring closet, many buildings will require cable runs greater than 100 meters. This necessitates the use of repeaters, or multiport repeaters called hubs, and the use of IDFs. Emphasize to the students that these requirements are a matter of both technology (the network will not work properly if the rules are violated) and standards (networks must be built according to various standards).</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>If the 100 m catchment area of a simple star topology wiring closet cannot provide enough coverage for all the devices that need to be networked, the star topology can be extended by using repeaters. Their purpose is to avoid the problem of signal attenuation. Generally speaking, when repeaters, or hubs, are used in this manner, they are located in additional wiring closets called IDFs, and are linked by networking media to a central hub located in another wiring closet called the MDF. TIA/EIA-568-A specifies the use of one of the following types of networking media:</p><ul type="disc"><li>100 Ohm UTP (four pair)</li><li>150 Ohm STP-A (two pair)</li><li>Two fiber (duplex) 62.5/125 碌m optical fiber</li><li>Multimode optical fiber</li></ul><p>The TIA/EIA recommends the use of CAT 5 UTP for horizontal cabling when using a simple star topology.</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.siemon.com/glossary/definitions.html">Cabling Glossary</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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