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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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Five media are of particular importance in this course -- STP, UTP, coaxial cable, optical fiber and wireless.</p> <p>The best way to introduce this term is to emphasize the medium you are using to talk to the students -- sound waves in air. Then do a show and tell with real cable samples and either sketches or overhead transparencies. Students should understand that networks often involve copper or optical medium, but that no medium at all is required in the case of wireless communication since electromagnetic waves travel just fine in vacuum.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>During your study of networking, you will hear references to the word <i>"medium"</i>. (Note: The plural form of medium is <i>media</i>.) In networking, a medium is a material through which data packets travel. It could be any of the following materials:<img border="0" src="../../../../../CHAPID=knet-v214aCH47502/RLOID=knet-v214aRLO47527/RIOID=knet-v214aRIO120883/knet/v214adataimage1/1.gif" width="12" height="12"><img border="0" src="../../../../../CHAPID=knet-v214aCH47502/RLOID=knet-v214aRLO47527/RIOID=knet-v214aRIO120883/knet/v214adataimage2/2.gif" width="12" height="12"><img border="0" src="../../../../../CHAPID=knet-v214aCH47502/RLOID=knet-v214aRLO47527/RIOID=knet-v214aRIO120883/knet/v214adataimage3/3.gif" width="12" height="12"><img border="0" src="../../../../../CHAPID=knet-v214aCH47502/RLOID=knet-v214aRLO47527/RIOID=knet-v214aRIO120883/knet/v214adataimage4/4.gif" width="12" height="12"></p><ul type="disc"><li>Telephone wires</li><li>Category 5 UTP (used for 10BASE-T Ethernet)</li><li>Coaxial cables (used for cable TV)</li><li>Optical fibers (thin glass fibers that carry light)</li><li>Wireless</li></ul><p>Communication without some type of wires or cables is called wireless or free-space communication. This is possible using electromagnetic (EM) waves. EM waves, which in a vacuum all travel at the speed of light, include power waves, radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays, and gamma rays.</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.rad.com/networks/1994/osi/osi.htm">The OSI Reference Model</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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