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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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In the water system, water is analogous to information (data), the various taps, valves, and fittings analogous to networking devices, and the width of the pipe analogous to bandwidth. In the highway system, the vehicles are analogous to information (data), the various traffic control devices are analogous to networking devices, and the quality of the highway -- particularly the number of lanes -- are analogous to bandwidth. In the audio analogy, the music is analogous to information (data), the various playback devices analogous to networking devices, and the analog bandwidth of the music (measured in kilohertz) is analogous to the digital bandwidth of the network. These are powerful analogies, which are commonly used in the networking field. A class demonstration or homework assignment might have students compare the quality of sound coming through a telephone, over an AM radio, over an FM radio, from a tape deck, and from a CD-player and reflecting on what the difference in quality is. Another example of analog bandwidth is the spacing of AM and FM radio stations -- a spectrum graph can show how a certain width of frequencies, centered around a carrier frequency, is required to send music or TV signals over a channel.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>Bandwidth is a very important element of networking, yet it can be rather abstract and difficult to understand. Following are three analogies that may help you picture what bandwidth is:</p><p>[Place the cursor of your mouse over the numbers in the animation to the left to view different bandwidth analogies.]</p><ol><li> <b>Bandwidth is like the width of a pipe.</b><img border="0" src="../../../../../CHAPID=knet-v214aCH47501/RLOID=knet-v214aRLO47522/RIOID=knet-v214aRIO120872/knet/v214adataimage1/1.gif" width="12" height="12"><p>Think of the network of pipes that brings water to your home and carries sewage away from it. Those pipes have different diameters. The main water pipe of the city may be 2 meters in diameter, whereas the kitchen faucet may be 2 centimeters. The width of the pipe measures the capacity of the pipe to carry water. In this analogy the water is like information and the width of the pipe is like bandwidth. In fact, many networking experts will talk in terms of "putting in bigger pipes". This means more bandwidth, which means a larger capacity to carry information.</p> </li><li> <b>Bandwidth is like the number of lanes on a highway.</b><img border="0" src="../../../../../CHAPID=knet-v214aCH47501/RLOID=knet-v214aRLO47522/RIOID=knet-v214aRIO120872/knet/v214adataimage2/2.gif" width="12" height="12"><p>Think about a network of roads that serves your city or town. There may be eight lane highways with exits onto two and three lane roads. This may then lead to two lane undivided streets, and eventually to your driveway. In this analogy, the number of lanes is like the bandwidth, and the number of cars is like the amount of information that can be carried.</p> </li><li> <b>Bandwidth is like the quality of sound in an audio system.</b><img border="0" src="../../../../../CHAPID=knet-v214aCH47501/RLOID=knet-v214aRLO47522/RIOID=knet-v214aRIO120872/knet/v214adataimage3/3.gif" width="12" height="12"><p>The sound is the information, and the quality of the sounds that you hear is the bandwidth. If you were asked to rank your preferences on how you would rather hear your favorite song, over the telephone, on an AM radio, on an FM radio, or on a CD. You would probably make the CD your first preference, then FM radio, AM radio, and finally telephone. The actual analog bandwidths for these are, respectively, 20 KHz, 15 KHz, 5 KHz, and 3 KHz.</p> </li></ol><p>Keep in mind that the true, actual meaning of bandwidth, in our context, is the maximum number of bits that can theoretically pass through a given area of space in specified amount of time (under the given conditions). The analogies we've used are only used here to make it easier to understand the concept of bandwidth.</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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