Carnegie Mellon 1 Internetworking+15#213:'Introduc0on'to'Computer'Systems'19th'Lecture,'Oct.'28,'2010'Instructors:''Randy'Bryant'and''Dave'O’Hallaron'Carnegie Mellon 2 A+Client3Server+Transac8on+Client+process+Server+process+1.#Client#sends#request#2.#Server##handles#request#3.#Server#sends#response#4.#Client##handles#response#Resource+ Most+network+applica8ons+are+based+on+the+client3server+model:+ A'server'process'and'one'or'more'client!processes' Server'manages'some'resource' Server'provides!service'by'manipula0ng'resource'for'clients' Server'ac0vated'by'request'from'client'(vending'machine'analogy)'Note:#clients#and#servers#are#processes#running#on#hosts##(can#be#the#same#or#different#hosts)#Carnegie Mellon 3 Hardware+Organiza8on+of+a+Network+Host+main+memory+I/O++bridge+MI+ALU+register+file+CPU+chip+system+bus+ memory+bus+disk++controller+graphics+adapter+USB+controller+mouse+keyboard+ monitor+disk+I/O+bus+Expansion+slots+network+adapter+network+Carnegie Mellon 4 Computer+Networks+ A+network+is+a+hierarchical+system+of+boxes+and+wires+organized+by+geographic al+proximity+ SAN'(System'Area'Network)'spans'cluster'or'machine'room' Switched'Ethernet,'Quadrics'QSW,'…' LAN'(Local'Area'Network)''spans'a'building'or'campus' Ethernet'is'most'prominent'example' WAN'(Wide'Area'Network)'spans'country'or'world' Typically'high#speed'point#to#point'phone'lines' An+internetwork#(internet)#is+an+interconnected+set+of+networks+ The'Global'IP'Internet'(uppercase'“I”)'is'the'most'famous'example'of'an'internet'(lowercase'“i”)' Let’s+see+how+an+internet+is+built+from+the+gr ound+up+Carnegie Mellon 5 Lowest+Level:+Ethernet+Segment+ Ethernet+segment+consists+of+a+collec 8 on+of+hosts+connected+by+wires+(twisted+pairs)+to+ a+hub# Spans+room+or+floor+in+a+building+ Opera8on+ Each'Ethernet'adapter'has'a'unique'48#bit'address'(MAC'address)' E.g.,'00:16:ea:e3:54:e6' Hosts'send'bits'to'any'other'host'in'chunks'called'frames! Hub'slavishly'copies'each'bit'from'each'port'to'every'other'port' Every'host'sees'every'bit' Note:'Hubs'are'on'their'way'out.'Bridges'(switches,'routers)'became'cheap'enough'to'replace'them'(means'no'more'broadcas0ng)'host+ host+ host+hub+100+Mb/s+100+Mb/s+port#Carnegie Mellon 6 Next+Level:+Bridged+Ethernet+Segment+ Spans+building+or+campus+ Bridges+cleverly+le arn+which+hosts+are+reachable+from+which+ports+and+then+selec8ve ly+copy+frames+from+port+to+port+host+host+ host+ host+ host+hub+ hub+bridge+100+Mb/s+ 100+Mb/s+host+host+hub+100+Mb/s+ 100+Mb/s+1+Gb/s+host+host+ host+bridge+host+host+hub+A+ B+C+X+Y+Carnegie Mellon 7 Conceptual+View+of+LANs+ For+simplicity,+hubs,+bridges,+and+wires+are+oZen+shown+as+a+collec8on+of+hosts+a[ached+to+a+single+wire:+host+ host+ host+...+Carnegie Mellon 8 Next+Level:+internets+ Mul8ple+incompa8ble+LANs+can+be+physically+connected+by+specialized+computers+called+routers# The+connected+networks+are+called+an+internet#host+ host+ host+...+host+ host+ host+...+WAN+ WAN+LAN#1#and#LAN#2#might#be#completely#different,#totally#incompaHble##(e.g.,#Ethernet#and#Wifi,#802.11*,#T1Plinks,#DSL,#…)#router+ router+ router+LAN+LAN+Carnegie Mellon 9 Logical+Structure+of+an+internet+ Ad+hoc+interconnec8on+of+networks+ No'par0cular'topology' Vastly'different'router'&'link'capaci0es' Send+packets+from+source+to+des8na8on+by+hopping+through+networks+ Router'forms'bridge'from'one'network'to'another' Different'packets'may'take'different'routes'router+router+router+router+router+router+host+host+Carnegie Mellon 10 The+No8on+of+an+internet+Protocol+ How+is+it+possible+to+send+bits+across+incompa8ble+LANs+and+WANs?+ Solu8on:++ protocol'socware'running'on'each'host'and'router'' smooths'out'the'differences'between'the'different'networks' Implements+an+internet+pr otocol+(i.e.,+set+of+rules)+ governs'how'hosts'and'routers'should'cooperate'when'they'transfer'data'from'network'to'network' TCP/IP'is'the'protocol'for'the'global'IP'Internet'Carnegie Mellon 11 What+Does+an+internet+Protocol+Do?+ Provides+a+naming+scheme+ An'internet'protocol'defines'a'uniform'format'for'host#addresses# Each'host'(and'router)'is'assigned'at'least'one'of'these'internet'addresses'that'uniquely'iden0fies'it' Provides+a+delivery+mechanism+ An'internet'protocol'defines'a'standard'transfer'unit'(packet)' Packet'consists'of'header!and'payload# Header:'contains'info'such'as'packet'size,'source'and'des0na0on'addresses' Payload:'contains'data'bits'sent'from'source'host!Carnegie Mellon 12 LAN2#Transferring+Data+Over+an+internet+protocol+soZware+client+LAN1+adapter+Host+A+LAN1#data+(1)+data+ PH+ FH1+(4)+data+ PH+ FH2+(6)+data+(8)+data+ PH+ FH2+ (5)+LAN2#frame#protocol+soZware+LAN1+adapter+LAN2+adapter+Router#data+ PH+(3)+ FH1+data+ PH+ FH1+(2)+internet#packet#LAN1#frame#(7)+ data+ PH+ FH2+protocol+soZware+server+LAN2+adapter+Host+B+PH:'Internet'packet'header'FH:'LAN'frame'header'Carnegie Mellon 13 Other+Issues+ We+are+glossing+over+a+number+of+important+ques8ons:+ What'if'different'networks'have'different'maximum'frame'sizes?'(segmenta0on)' How'do'routers'know'where'to'forward'frames?' How'are'routers'informed'when'the'network'topology'changes?' What'if'packets'get'lost?' These+(and+other)+ques8ons+are+addressed+by+the+area+of++systems+known+as+computer#networking#Carnegie Mellon 14 Global+IP+Internet+ Most+famous+example+of+an+internet+ Based+on+the+TCP/IP+pr otocol+family+ IP'(Internet'protocol)':'' Provides'basic!naming!scheme!and'unreliable'delivery!capability''of'packets'(datagrams)'from'host#to#host' UDP'(Unreliable'Datagram'Protocol)' Uses'IP'to'provide'unreliable'datagram'delivery'from''process4to4process! TCP'(Transmission'Control'Protocol)' Uses'IP'to'provide'reliable'byte'streams'from'process#to#process'over'connec0ons' Accessed+via+a+mix+of+Unix+file+I/O+and+func8ons+from+the+sockets#interface+Carnegie Mellon 15 Hardware+and+SoZware+Organiza8on++of+an+Internet+Applica8on+TCP/IP+Client+Network+adapter+Global+IP+Internet+TCP/IP+Server+Network+adapter+Internet#client#host#
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