Chapter 11 Network Infrastructure

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1、Chapter11NetworkInfrastructure11.1NetworkTopologyThewordtopologyiscommonlyusedtodiscussthepropertiesofvarioustypesofnetworks.Thefollowingfourtypesofphysicaltopologiesarefrequentlyusedincomputernetworking:Startopology,Bustopology,Ringtopology,Hybridtopology.11.1.1.StarTop

2、ologyInastartopology,eachdeviceconnectstoacentralpointviaapoint-to-pointlink.Thestarnetworktopologyworkswellwhenworkstationsareatscatteredpoints.Itiseasytoaddorremoveworkstations.Butstartopologyhasthefollowingdisadvantages:(1)ifthecentralcomputer(hub)goesdown,theentirene

3、tworkwillsufferdegradedperformanceorcompletefailure.(2)Becausepoint-to-pointwiringisutilizedforeachnode,morecableisrequired.11.1.2.RingTopologyInaringtopology,thenodesareconnectedinaclosedloopconfiguration.Ringtopologyhasthefollowingadvantage:(1)Eachrepeaterduplicatesthe

4、datasignalssothatverylittlesignaldegradationoccurs.(2)Theringtopologymayproveoptimumwhensystemrequirementsaremodestandworkstationsareatscatteredpoints.11.1.3.BusTopologyInabustopology,alldevicesattachtothesamepublictransmissionmedium.Allbusesareimplementedusingelectrical

5、cable,usuallycoaxialcable,andtheendsofthecablemustbeterminatedwithaterminatingresistorthatmatchestheimpedanceofthecable.Thereareseverallimitationstothebusnetworktopology.(1)Thelengthofthebusislimitedbycableloss.(2)Thepubliccablebreakscandisabletheentiresegment.Theusualtr

6、ansmissionmediainbustopologyiscoaxialcable.11.1.4.HybridTopologyThehybridtopologyschemecombinesmultipletopologiesintoonelargetopology(seefigure11.1).Thehybridnetworkiscommoninlargewide-areanetworks.Hybridtopologyhasthefollowingadvantages:(1)Onecompanycancombinethebenefit

7、sofseveraldifferenttypesoftopologies.(2)Workgroupefficiencyandtrafficcanbecustomized.Thelimitationtohybridtopologyis:Devicesononetopologycannotbeplacedintoanothertopologywithoutsomehardwarechanges.Fig.11.1ThenetworkofHybridtopology11.2TheBasicsofOSIReferenceModelandTCP/I

8、PModel11.2.1.OSIReferenceModelOpenSystemsInterconnection(OSI)isastandardreferencemodelforcommunicationb