生命很惊慌地带女儿去看医生

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1、FastEthernetandGigabitEthernet1Networks:FastEthernetFastEthernet(100BASE-T)Howtoachieve100Mbpscapacity?MediaIndependentInterfaceprovidesthreechoices.LLCMACConvergenceSublayerMediaDependentSublayerMediaIndependentInterfaceDataLinkLayerPhysicalLayerMII2Networks:FastEthernetFastEthe

2、rnet[IEEE802.3u]ThreeChoicesFigure4-21.TheoriginalfastEthernetcabling.Conceptfacilitatedby10Mbps/100MbpsAdapterCards3Networks:FastEthernet100BASET4Networks:FastEthernetFastEthernetDetailsUTPCablehasa30MHzlimitNotfeasibletouseclockencoding(i.e.,NOManchesterencoding)Insteadusebiten

3、codingschemeswithsufficienttransitionsforreceivertomaintainclocksynchronization.5Networks:FastEthernet100BASET4CanusefourseparatetwistedpairsofCat3UTPUtilizethreepairinbothdirections(at331/3Mbps)withotherpairforcarriersense/collisiondetection.Three-levelternarycodeisused8B/6T.Pri

4、ortotransmissioneachsetof8bitsisconvertedinto6ternarysymbols.6Networks:FastEthernet100BASET4Thesignalingratebecomes100x6/8------------=25MHz3Threesignallevels:+V,0,-VCodewordsareselectedsuchthatlineisd.c.balancedAllcodewordshaveacombinedweightof0or1.7Networks:FastEthernet100BASET

5、436=729possiblecodewords.Only256codewordsarerequires,hencetheyareselected:Toachieved.c.balanceAssumingallcodewordshaveatleasttwosignaltransitionswithinthem(forreceiverclocksynchronization).Tosolved.c.wander,wheneverastringofcodewordswith+1aresent,alternatecodewords(invertedbefore

6、transmission)areused.Toreducelatency,ternarysymbolsaresentstaggeredonthethreelines.8Networks:FastEthernet100BASET4EthernetInterframegapof9.6microsecondsbecomes960nanosecondsinFastEthernet.100m.maxdistancetohub;200metersbetweenstations.MaximumoftwoClassIIrepeaters.9Networks:FastEt

7、hernet100BaseTXUsestwopairoftwistedpair,onepairfortransmissionandonepairforreception.UseseitherSTPorCat5UTP.UsesMTL-3signalingschemethatinvolvesthreevoltages.Uses4B/5Bencoding.Thereisaguaranteedsignaltransitionatleasteverytwobits.10Networks:FastEthernet100BASEFXUsestwoopticalfibe

8、rs,onefortransmissionandoneforreception.