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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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Hubs are multiport repeaters, hence Layer 1 devices, and they regenerate and retime signals while providing inexpensive connectivity for numbers of networking devices.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>The purpose of a hub is to regenerate and retime network signals. This is done at the bit level to a large number of hosts (for example, 4, 8, or even 24) using a process known as concentration. <img border="0" src="../../../../../CHAPID=knet-v214aCH47503/RLOID=knet-v214aRLO47534/RIOID=knet-v214aRIO121107/knet/v214adataimage1/1.gif" width="12" height="12"><img border="0" src="../../../../../CHAPID=knet-v214aCH47503/RLOID=knet-v214aRLO47534/RIOID=knet-v214aRIO121107/knet/v214adataimage2/2.gif" width="12" height="12"> You will notice that the definition of a hub is very similar to the definition of a repeater, which is why a hub is also known as a multiport repeater. In fact, a hub is nothing more than a repeater with more than two ports. Two reasons for using hubs are to create a central connection point for the wiring media, and increase the reliability of the network. The reliability of the network is increased by allowing any single cable to fail without disrupting the entire network. This differs from the bus topology where having one cable fail will disrupt the entire network. Hubs are considered Layer 1 devices because they only regenerate the signal and broadcast it out all of their ports (network connections), except for the port on which the signal was received.<img border="0" src="../../../../../CHAPID=knet-v214aCH47503/RLOID=knet-v214aRLO47534/RIOID=knet-v214aRIO121107/knet/v214adataimage3/3.gif" width="12" height="12"></p><p>There are different classifications of hubs in networking. The first classification is active or passive hubs. Most modern hubs are active; they take energy from a power supply to regenerate network signals. Some hubs are called passive devices because they merely split the signal for multiple users, like using a "Y" cord on a CD player to use more than one set of headphones. Passive hubs do not regenerate bits, so they do not extend the cable length. They simply allow two or more hosts to connect to the same cable segment.</p><p>Another classification of hubs is intelligent or dumb. Intelligent hubs have console ports, which means they can be programmed to manage network traffic. Dumb hubs simply take an incoming networking signal and repeat it to every other port without the ability to do any management.</p><p>The role of the hub in a Token Ring network is played by a Media Access Unit (MAU). Physically it resembles a hub, but token-ring technology is very different, as you will learn later. In FDDIs, the MAU is called a concentrator. MAUs are also Layer 1 devices.</p><p>The symbol for a hub is not standardized. You will use the symbol shown here throughout this curriculum.<img border="0" src="../../../../../CHAPID=knet-v214aCH47503/RLOID=knet-v214aRLO47534/RIOID=knet-v214aRIO121107/knet/v214adataimage1/1.gif" width="12" height="12"></p><p>For more information about commercially available hubs, visit the websites listed below.</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.blackbox.com/">Blackbox Network Services</a></span></td> </tr> <tr> <td valign="middle" width="8%"> </td><td valign="middle" width="92%"><span class="smtext"><a target="_blank" href="http://www.warehouse.com/">Micro Warehouse</a></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/1997/nettut/hub.html">Hubs</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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