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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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Physical media is Layer 1 in the OSI model, and is the material (or space) where networking signals travel.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>The symbols for media vary. For example: the Ethernet symbol is typically a straight line with perpendicular lines projecting from it; the token-ring network symbol is a circle with hosts attached to it; and for FDDI, the symbol is two concentric circles with attached devices.</p><p>The basic function of media is to carry a flow of information, in the form of bits and bytes, through a LAN. Other than wireless LANs (that use the atmosphere, or space, as the medium) and the new PANs (personal area networks, that use the human body as a networking medium), networking media confine network signals to a wire, cable, or fiber. Networking media are considered Layer 1 components of LANs.</p><p>You can build computer networks with many different media types. Each media has advantages and disadvantages. What is an advantage for one media (Category 5 cost) might be a disadvantage for another (fiber-optic cost). There are several factors to consider when weighing the advantages of different media:</p><ul type="disc"><li>Cable length</li><li>Cost</li><li>Ease of installation</li></ul><p>Coaxial cable, optical fiber, and even free space can carry network signals, however, the principal medium you will study is called Category 5 unshielded twisted-pair cable (CAT 5 UTP).</p><p>To find out more about commercially available media, 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> </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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