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1、SectionBAGuidetoNetworkTopologyAnetworktopologyishowcomputers,printers,andotherdevicesareconnectedoveranetwork.Itdescribesthelayoutowires,devices,androutingpaths.Essentiallytherearesixdifferentcommontopologiesyoushouldfamiliarizeyouselfwith:bus,ring,star,exten
2、dedstar,hierarchical,andmesh.Ⅰ.BusTopologyThebustopologywasfairlypopularintheearlyyearsofnetworking.It’seasytosetup-nottomentioninexpensive.Alldevicesonthebustopologyareconnectedusingasinglecable.Ifyouneedhelprememberinghowthebustopologyoperates,thinkofitasthe
3、routeabustakesthroughoutacity.Itisextremelyimportanttonotethatbothendsofthemaincableneedtobeterminated.Ifthereisnoterminator,thesignalwillbouncebackwhenitreachestheend.Theresult:abunchofcollisionsandnoisethatwilldisrupttheentirenetwork.Thebustopologyislesscomm
4、onthesedays.Infact,thistopologyiscommonlyusedinnetworkcomputersviacoaxialcable—when’sthelasttimeyoucansayyouhavedonethat?Ⅱ.RingTopologyTheringtopologyisaveryinterestingtopologyindeed.Itisalotmorecomplexthanitmayseem—itlookslikejustabunchofcomputersconnectedina
5、circle!Butbehindthescenes,theringtopologyisprovidingacollision-freeandredundantnetworkingenvironment.Notethatsincethereisnoendonaringtopology,noterminatorsarenecessary.Aframetravelsalongthecircle,stoppingateachnode.Ifthatnodewantstotransmitdata,itaddsdestinati
6、onaddressanddatainformationtotheframe.Theframethentravelsaroundthering,searchingforthedestinationnode.Whenit’sfound,thedataistakenoutoftheframeandthecirclecontinues.Butwait—itgetsbetter!Wehavetwotypesofringtopologiesinnetworking:theonewejustreviewed,anddual-ri
7、ngtopology.Inadual-topology,weusetworingsinsteadofone.Thiscreatesasenseofredundancysothatifanypointinthenetworkfails,thesecondringwill(hopefully)beabletopickuptheslack.Ifbothringsweretofailatseparatelocations,wecanevenusetheoppositeringateachpointto“patch”thed
8、ownednode.InthediagramontherightinFigure8B-1,youcanseethatalthoughtheouterringandinnerringfailedatseparatepartsofthenetwork,thankstoredundancy,thenetworkisstillfullyoperational.Thi
