Internetworking December 12, 2000 Topics• Protocol layering and encapsulation• Internetworking with hubs, bridges, androuters• The Internet Protocol (IP)• The global Internetclass30.ppt15-213“The course that gives CMU its Zip!”CS 213 F’00– 2 –class30.pptTypical computer systemLocal/IO BusLocal/IO BusMemoryMemoryNetworkadapterNetworkadapterIDE diskcontrollerIDE diskcontrollerVideoadapterVideoadapterDisplayDisplayNetworkNetworkProcessorProcessorInterruptcontrollerInterruptcontrollerSCSIcontrollerSCSIcontrollerSCSI busSCSI busSerial port controllerSerial port controllerParallel portcontrollerParallel portcontrollerKeyboardcontrollerKeyboardcontrollerKeyboardKeyboardMouseMousePrinterPrinterModemModemdiskdisk cdromCS 213 F’00– 3 –class30.pptGeneric networkInterconnect (wires, repeaters, bridges, and routers)Interconnect (wires, repeaters, bridges, and routers)softwaresoftwarehardwarehardwaresoftwaresoftwarehardwarehardwarelink link linkhost hostprotocol stacknetwork adapter/interface cardOS codesoftwaresoftwarehardwarehardwareCS 213 F’00– 4 –class30.pptProtocolsA protocol defines the format of packets and the rulesfor communicating them across the network.Different protocols provide different levels of service:• simple error correction (ethernet)• uniform name space, unreliable best-effort datagrams (host-host) (IP)• reliable byte streams (TCP)• unreliable best-effort datagrams (process-process) (UDP)• multimedia data retrieval (HTTP)Crucial idea: protocols leverage off of the capabilities ofother protocols.CS 213 F’00– 5 –class30.pptProtocol layeringProtocols provide specialized services byrelying on services provided by lower-level protocols (i.e., they leverage lower-level services).Reliablebyte streamdelivery(process-process)Unreliablebest effortdatagramdelivery(host-host)Unreliablebest effortdatagramdelivery(process-process)User application program (FTP, Telnet, WWW, email)User application program (FTP, Telnet, WWW, email)User datagram protocol(UDP)User datagram protocol(UDP)Transmission control protocol (TCP)Transmission control protocol (TCP)Internet Protocol (IP)Internet Protocol (IP)Network interface (ethernet)Network interface (ethernet)hardwarehardwarePhysicalconnectioninterface between usercode and OS code(Sockets interface)CS 213 F’00– 6 –class30.pptEncapsulationTCP segment headerTCP segment headerdatadatadatadataEthernet frameheaderEthernet frameheaderIP datagramheaderIP datagramheaderTCP segment headerTCP segment headerdatadataIP datagramheaderIP datagramheaderTCP segment headerTCP segment headerdatadataApplication programTCPIPAdapterNetworkOS codeUser codeUser Interface (API)OS/adapter interface(exception mechanism)Adapter/Network interfaceCS 213 F’00– 7 –class30.pptBasic network typesSystem area network(SAN)• same room (meters)• 300 MB/s Cray T3ELocal area network (LAN)• same bldg or campus(kilometers)• 10 Mb/sEthernet• 100 Mb/s Fast Ethernet• 100 Mb/s FDDI• 150 Mb/s OC-3 ATM• 622 Mb/s OC-12 ATMMetropolitan area network(MAN)• same city (10’s of kilometers)• 800 Mb/s Gigabit NectarWide area network (WAN)• nationwide or worldwide(1000’s of kilometers)• telephone system• 1.544 Mb/s T1 carrier• 44.736 Mb/s T3 carrier• Global InternetCS 213 F’00– 8 –class30.pptThe internetworking idea(Kahn, 1972)Build a single network (an interconnected set ofnetworks, or internetwork, or internet) out of a largecollection of separate networks.• Each network must stand on its own, with no internal changesallowed to connect to the internet.• Communications should be on a best-effort basis.• “black boxes” (later called routers) should be used to connect thenetworks.• No global control at the operations level.CS 213 F’00– 9 –class30.pptInternetworking challengesChallenges:• heterogeneity–lots of different kinds of networks (Ethernet, FDDI, ATM, wireless,point-to-point)–how to unify this hodgepodge?• scale–how to provide uniques names for potentially billions of nodes?(naming)–how to find all these nodes? (forwarding and routing)Note: internet refers to a general idea, Internet refers toa particular implementation of that idea (The global IPInternet).CS 213 F’00– 10 –class30.pptInternetworking with repeatersrrrrRepeaters (also called hubs)(r in the figure) directlytransfer bits from their inputsto their outputsCS 213 F’00– 11 –class30.pptInternetworking with repeatersHost on network AHost on network BTelnet, FTP,HTTP, emailapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata link10Base-TphysicalRepeater(forwards bits)CS 213 F’00– 12 –class30.pptInternetworking with repeaters:Pros and consPros• Transparency–LANS can be connected without any awareness from the hosts.• Useful for serving multiple machines in an office from one ethernetoutlet.Cons• Not scalable–ethernet standard allows only 4 repeaters.–more than 4 would introduce delays that would break contentiondetection.• No heterogeneity–Networks connected with repeaters must have identical electricalproperties.CS 213 F’00– 13 –class30.pptInternetworking with bridgesbbbbBridges (b In the figure)maintain a cache of hosts ontheir input segments.Selectively transferethernet frames from theirinputs to their outputs.CS 213 F’00– 14 –class30.pptInternetworking with bridgesHost on network AHost on network BTelnet, FTP,HTTP, emailapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkCSMA/CD10Base-TphysicalBridge(forwards ethernetframes)CS 213 F’00– 15 –class30.pptInternetworking with bridges:Pros and consPros• Transparency–LANS can be connected without any awareness from the hosts–popular solution for campus-size networksCons• Transparency can be misleading–looks like a single Ethernet segment, but really isn’t–packets can be dropped, latencies vary• Homogeneity–can only support networks with identical frame headers (e.g.,Ethernet/FDDI)–however, can connect different speed Ethernets• Scalability–tens of networks only»bridges forward all broadcast frames»increased latencyCS 213 F’00– 16 –class30.pptInternetworking with routersDef: An internetwork (internet for short) is an arbitrarycollection of physical networks interconnected byrouters to provide some sort of host-to-host packetdelivery service.internetinternethosthosthosthosthosthosthosthostCS 213 F’00– 17 –class30.pptBuilding an
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