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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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eval('top.frames.main_frame.location.href="'+ContentRef+'referencecontroller_crf.html"'); chapter = "knet-v214aCH47503"; ch_dash = chapter.indexOf('-'); ch_sub1 = chapter.substring(0,ch_dash); ch_sub2 = chapter.substring(ch_dash+1); params = "CHAPID=" + chapter + "/RLOID=" + "knet-v214aRLO47535" + "/RIOID=" + "knet-v214aRIO121113"; returnRef = "../../../../../"+ params + "/"+ ch_sub1 +"/"+ ch_sub2 +"/pageframeset.html"; top.prevPage = returnRef; } function launchFile(filepath) { newWindow = window.open(filepath,"","top=70,left=120,width="+(screen.width*.50)+",height="+(screen.height*.50)+",resizable=yes,scrollbars=yes,toolbar=yes,menubar=yes,status=yes"); /* if (is.ie && filepath.lastIndexOf(".pdf") != -1) { pageTimer = setInterval("winLoadCheck()", 1000); } */ } function winLoadCheck() { if (newWindow.document.readyState == 'complete') { clearInterval(pageTimer); newWindow.location.reload(); } } // BrowserCheck Object // provides most commonly needed browser checking variables // 19990326 // Copyright (C) 1999 Dan Steinman // Distributed under the terms of the GNU Library General Public License // Available at http://www.dansteinman.com/dynapi/ function BrowserCheck() { var b = navigator.appName if (b=="Netscape") this.b = "ns" else if (b=="Microsoft Internet Explorer") this.b = "ie" else this.b = b this.v = parseInt(navigator.appVersion) this.ns = (this.b=="ns" && this.v>=4) this.ns4 = (this.b=="ns" && this.v==4) this.ns5 = (this.b=="ns" && this.v==5) this.ie = (this.b=="ie" && this.v>=4) this.ie4 = (navigator.userAgent.indexOf('MSIE 4')>0) this.ie5 = (navigator.appVersion.indexOf('MSIE 5.0')>0) this.ie55 = (navigator.appVersion.indexOf('MSIE 5.5')>0) if (this.ie5) this.v = 5 this.min = (this.ns||this.ie) } // automatically create the "is" object is = new BrowserCheck()</script> </head> <body onLoad="window.focus();" alink="#000000" vlink="#000000" link="#000000" bgcolor="#E7E7E7" background="../../../../../images/ccna/common/bg.gif"> <table width="100%" cellspacing="0" cellpadding="2" border="0"><tr> <td bgcolor="#000000"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td class="rlohdr"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td valign="top" class="rlohdr">3.2</td><td width="100%" class="rlohdr"> <table width="90%" cellpadding="0" cellspacing="0" border="0"> <tr> <td class="rlohdr">Evolution of Network Devices</td> </tr> </table> </td> </tr> <tr> <td bgcolor="#000000"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td class="riohdr"><img height="1" width="2" border="0" src="../../../../../images/ccna/common/transdot.gif"></td><td valign="top" class="riohdr">3.2.1</td><td width="100%" class="riohdr"> <table width="90%" cellpadding="0" cellspacing="0" border="0"> <tr> <td class="riohdr">Evolution of network devices</td> </tr> </table> </td> </tr> <tr> <td colspan="4"> <table width="90%" cellspacing="0" cellpadding="0" border="0"> <tr> <td class="smtext"> <p> </p><table cellpadding="0" cellspacing="0" width="100%" border="0" xmlns:java="http://xml.apache.org/xslt/java"> <tr> <td width="100%"><img height="10" width="1" border="0" src="../../../../../images/ccna/common/transdot.gif"></td> </tr> <tr> <td width="100%"> <table bgcolor="#000000" bordercolor="#000000" cellspacing="0" bordercolorlight="#000000" width="100%" border="0"> <tr> <td width="100%"> <table bgcolor="#FFFFFF" cellspacing="0" cellpadding="2" width="100%" border="0"> <tr> <td valign="middle"><img height="22" width="22" border="0" src="../../../../../images/ccna/common/inotes.gif"></td><td valign="middle"><span class="cstitle">Instructor Note</span></td> </tr> <tr> <td valign="top"> </td><td valign="top"><span class="cstext"> <p>The purpose of this target indicator is to make the point that the Internet is undergoing an unprecedented rate of introduction into society. The graph shows the exponential increase in the usage of the Internet. A related growth curve has been described and observed for years -- known as Moore's Law, it loosely states that processor power doubles every 18 months to two years. Since raw processor power is part of the technological basis for data networks, this growth helps fuel the exponential growth of Internet user and electronic commerce (business done over the Internet). Students should be aware of the revolution they are living through, and into which they are being educated to participate.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>The history of computer networking is complex, involving many people from all over the world over the past thirty years. This is a simplified view of how networking devices have evolved. The processes of invention and commercialization are far more complicated, but it is helpful to look at the problems that each networked device solved and the problems that still remain.</p><p>In the 1940s, computers were huge electromechanical devices that were prone to failure. In 1947, the invention of a semiconductor transistor opened up many possibilities for making smaller, more reliable computers. In the 1950s, mainframe computers, run by punched card programs, began to be commonly used by large institutions. In the late 1950s, the integrated circuit - that combined several, many, and now millions, of transistors on one small piece of semiconductor - was invented. Through the 1960s, mainframes with terminals were commonplace, and integrated circuits became more widely used.</p><p>In the late 60s and 70s, smaller computers, called minicomputers (though still huge by today's standards), came into existence. In 1978, the Apple Computer company introduced the personal computer. In 1981, IBM introduced the open architecture personal computer. The user friendly Mac, the open architecture IBM PC, and the further micro miniaturization of integrated circuits led to widespread use of personal computers in homes and businesses. As the late 1980s began, computer users, with their stand alone computers, started to share data (files) and resources (printers). People asked, why not connect them?</p><p>While all of this was happening, telephone systems continued to improve. Especially in the areas of switching technology and long distance service (because of new technologies like microwaves and optical fibers), a worldwide, reliable telephone system evolved.</p><p>Starting in the 1960s and continuing through the 70s, 80s, and 90s, the Department of Defense (DoD) developed large, reliable, wide area networks (WANs). Some of their technology was used in the development of LANs, but more importantly, the DoDs WAN eventually became the Internet.</p><p>To help you understand the next technological advancement, consider the following problem. Somewhere in the world, there were two computers that wanted to communicate with each other. In order to do so, they both needed some kind of device that could talk to the computers and the media (the NIC), and some way for the messages to travel (medium).</p><p>Suppose, also, that the computers wanted to communicate with other computers that were a great distance away. The answer to this problem came in the form of repeaters and hubs. The repeater (an old device used by telephone networks) was introduced to enable computer data signals to travel farther. The multiport repeater, or hub, was introduced to enable a group of users to share files, servers and peripherals. You might call this a workgroup network.</p><p>Soon, workgroups wanted to communicate with other workgroups. Because hubs broadcast all messages to all ports, regardless of destination, network congestion increased rapidly with increases in the number of workgroups and hosts. The bridge was invented to segment the network and to introduce some traffic control.</p><p>The best feature of the hub (concentration /connectivity) and the best feature of the bridge (segmentation) were combined to produce a switch. It had numerous ports, but allowed each port to pretend it had a connection to the other side of the bridge, thus allowing many users and efficient communications.</p><p>In the mid 1980s, special-purpose computers, called gateways (and then routers) were developed. These devices allowed the interconnection of separate LANs. Internetworks were created. The DoD already had an extensive internetwork, but the commercial availability of routers, which carried out best path selections and switching for data from many protocols, caused the explosive growth of networks that we are experiencing today.</p><p>With the arrival of the new century, the next step is convergence of computer and communications technology. This allowed convergence of voice, video, and data, which have traditionally traveled via different systems, into one information stream.</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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