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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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The Ethernet family is the most popular LAN technology in use today and students should develop a solid understanding of it. The graphic presents the details of the lower 2 levels of the OSI model as they pertain to Ethernet.</p> <p>This TI relates to CCNA Certification Exam Objectives #51, #55, and #56.</p> </span></td> </tr> </table> </td> </tr> </table> </td> </tr> </table><p>Ethernet is the most widely used local area network (LAN) technology. Ethernet was designed to fill the middle ground between long-distance, low-speed networks and specialized, computer room networks carrying data at high speeds for very limited distances. Ethernet is well suited to applications where a local communication medium must carry sporadic, occasionally heavy traffic at high peak data rates.</p><p>Ethernet network architecture has its origins in the 1960s at the University of Hawaii. This is where the access method that is used by Ethernet, carrier sense multiple access/collision detection (CSMA/CD), was developed. Xerox Corporation's Palo Alto Research Center (PARC) developed the first experimental Ethernet system in the early 1970s. This was used as the basis for the Institute of Electrical and Electronic Engineers (IEEE) 802.3 specification released in 1980.</p><p>Shortly after the 1980 IEEE 802.3 specification, Digital Equipment Corporation, Intel Corporation, and Xerox Corporation jointly developed and released an Ethernet specification, Version 2.0, that was substantially compatible with IEEE 802.3. Together, Ethernet and IEEE 802.3 currently maintain the greatest market share of any LAN protocol. Today, the term Ethernet is often used to refer to all carrier sense multiple access/collision detection (CSMA/CD) LAN that generally conform to Ethernet specifications, including IEEE 802.3.</p><p>Ethernet and IEEE 802.3 specify similar technologies. Both are CSMA/CD LANs. Stations on a CSMA/CD LAN can access the network at any time. Before sending data, CSMA/CD stations listen to the network to determine if it is already in use. If it is, then they wait. If the network is not in use, the stations transmit. A collision occurs when two stations listen for network traffic, hear none, and transmit simultaneously. In this case, both transmissions are damaged, and the stations must retransmit at some later time. Backoff algorithms determine when the colliding stations can retransmit. CSMA/CD stations can detect collisions, so they know when they must retransmit.</p><p>Both Ethernet and IEEE 802.3 LANs are broadcast networks. This means every station can see all of the frames, regardless of whether they are the intended destination of that data. Each station must examine the received frames to determine if they are the destination. If so, the frame is passed to a higher layer protocol within the station for appropriate processing.</p><p>Differences between Ethernet and IEEE 802.3 LANs are subtle. Ethernet provides services corresponding to Layer 1 and Layer 2 of the OSI reference model. IEEE 802.3 specifies the physical layer, Layer 1, and the channel access portion of the data link layer, Layer 2, but does not define a Logical Link Control protocol. Both Ethernet and IEEE 802.3 are implemented through hardware. Typically, the physical part of these protocols is either an interface card in a host computer or circuitry on a primary circuit board within a host computer.</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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