Network technology April 11, 2000Course Theme“Harsh Realities” of Computer ScienceTypical computer systemSimple exampleQuestions about simple exampleGeneric networkProtocolsProtocol layeringEncapsulationTransmission mediaBasic network typesAT&T Telephone HierarchyConnecting distant computers with modemsModulating digital signalsQuadrature amplitude modulation (QAM)Conventional ModemsT1 carrier (1.544 Mb/s)56KB “Modems”Comparison with other connection technologiesBasic Internet componentsThe Internet circa 1993The Internet backbone (circa 1993)Current NAP-based Internet architectureInternet connection hierarchyNetwork access points (NAPs)PowerPoint PresentationCost of Frame Relay connectionsCost of T1 connectionsCost of T3 connectionsEthernetEthernet cablingRepeaters vs bridgesEthernet packet (frame) formatEthernet receiving algorithmEthernet sending algorithm (CSMA/CD)Binary exponential backoffWhy the 64 byte minimum packet size?Ethernet pros and consNetwork technologyApril 11, 2000Topics•Fundamental concepts–protocols, layering, encapsulation, network types•Wide area networks–phone lines and modems–Internet backbones•Local area networks–Ethernet15-213class23.pptCS 213 S’00– 2 –class23.pptCourse ThemeAbstraction is good, but don’t forget reality!Earlier courses to date emphasize abstraction•Abstract data types•Asymptotic analysisThese abstractions have limits•Especially in the presence of bugs•Need to understand underlying implementationsUseful outcomes•Become more effective programmers–Able to find and eliminate bugs efficiently–Able to tune program performance•Prepare for later “systems” classes–Compilers, Operating Systems, Networks, Computer ArchitectureCS 213 S’00– 3 –class23.ppt“Harsh Realities” of Computer Science•Int’s are not integers; float’s are not reals–Must understand characteristics of finite numeric representations•You’ve got to know assembly–Basis for understanding what really happens when execute program•Memory matters–Memory referencing bugs especially difficult»Violates programming language abstraction–Significant performance issues»E.g., cache effects•There’s more to performance than asymptotic complexity–Constant factors also matter•Computers do more than execute programs–Get data in and out–Communicate with each other via networksCS 213 S’00– 4 –class23.pptTypical computer systemLocal/IO BusLocal/IO BusMemoryMemoryNetworkadapterNetworkadapterIDE diskcontrollerIDE diskcontrollerVideoadapterVideoadapterDisplayDisplayNetworkNetworkProcessorProcessorInterruptcontrollerInterruptcontrollerSCSIcontrollerSCSIcontrollerSCSI busSCSI busSerial port controllerSerial port controllerParallel portcontrollerParallel portcontrollerKeyboardcontrollerKeyboardcontrollerKeyboardKeyboardMouseMousePrinterPrinterModemModemdiskdisk cdromCS 213 S’00– 5 –class23.pptSimple exampleStarting Point: Want to send bits between 2 computers•FIFO (First-in First-out) queue (buffer) on each end•Can send both ways (“full duplex”)•Name for standard group of bits sent: “packet”•Packet format and rules for communicating them (“protocol”)Simple request/response protocol and packet format:0/1 data/address0: please send the data word at “address”1: here is the data word you asked for.headerpayloadCS 213 S’00– 6 –class23.pptQuestions about simple exampleWhat if more than 2 computers want to communicate?•Need an interconnect? Need computer address field in packet?What if the machines are far away?•WAN vs LANHow do multiple machines share the interconnect?•multiple paths? arbitration? congestion control?What if a packet is garbled in transit?•Add error detection field in packet?What if a packet is lost?•More elaborate protocols to detect loss?What if multiple processes per machine?•one queue per process? separate field in packet to identify process?Warning: You are entering a buzzword-rich environment!!!CS 213 S’00– 7 –class23.pptGeneric networkInterconnect (wires, repeaters, bridges, etc)Interconnect (wires, repeaters, bridges, etc)softwaresoftwarehardwarehardwaresoftwaresoftwarehardwarehardwarelink link linkhost hostprotocol stacknetwork adapter/interface cardOS codesoftwaresoftwarehardwarehardwareCS 213 S’00– 8 –class23.pptProtocolsA protocol defines the format of packets and the rules for 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 of other protocols.CS 213 S’00– 9 –class23.pptProtocol layeringProtocols provide specialized services by relying on services provided by lower-level protocols (i.e., they leverage lower-level services).Reliable byte streamdelivery(process-process)Unreliablebest effort datagramdelivery(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)hardwarehardwarePhysical connectioninterface between user code and OS code(Application program interface (API))CS 213 S’00– 10 –class23.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 S’00– 11 –class23.pptTransmission media2 insulated copper wirestwisted pair:twisted pair:(10 Mb/s at 5 km)stiff copper wireinsulatorbraided outer conductorplastic covercoaxial cable:coaxial cable:(1-2 Gb/s at 1 km)silicalight sourcefiber:fiber:(100-200 Gb/s at 1 km)station wagon full of mag tapes hurtling down the highway every hour:station wagon full of mag tapes hurtling down the highway every hour:(15 Gb/s at 1 hour)7 GBytes/tape1000 tapes/station wagon
View Full Document
Unlocking...