InternetworkingMay 1, 2001 Topics• Protocol layering and encapsulation• Internetworking with hubs, bridges, and routers• The Internet Protocol (IP)• The global Internetclass30.ppt15-213“The course that gives CMU its Zip!”CS 213 S’01– 2 –class30.pptTypical computer systemLocal/IO BusMemoryNetworkadapterIDE diskcontrollerVideoadapterDisplayNetworkProcessorInterruptcontrollerSCSIcontrollerSCSI busSerial port controllerParallel portcontrollerKeyboardcontrollerKeyboard Mouse PrinterModemdiskdisk cdromCS 213 S’01– 3 –class30.pptGeneric networkInterconnect (wires, repeaters, bridges, and routers)softwarehardwaresoftwarehardwarelink link linkhost hostprotocol stacknetwork adapter/interface cardOS codesoftwarehardwareCS 213 S’01– 4 –class30.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’01– 5 –class30.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 effortdatagramdelivery(host-host)Unreliablebest effortdatagramdelivery(process-process)User application program (FTP, Telnet, WWW, email)User datagram protocol(UDP)Transmission control protocol (TCP)Internet Protocol (IP)Network interface (ethernet)hardwarePhysical connectioninterface between user code and OS code(Sockets interface)CS 213 S’01– 6 –class30.pptEncapsulationTCP segment headerdatadataEthernet frameheaderIP datagramheaderTCP segment headerdataIP datagramheaderTCP segment headerdataApplication programTCPIPAdapterNetworkOS codeUser codeUser Interface (API)OS/adapter interface(exception mechanism)Adapter/Network interfaceCS 213 S’01– 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 S’01– 8 –class30.pptThe internetworking idea (Kahn, 1972)Build a single network (an interconnected set of networks, or internetwork, or internet) out of a large collection of separate networks.• Each network must stand on its own, with no internal changes allowed to connect to the internet.• Communications should be on a best-effort basis.• “black boxes” (later called routers) should be used to connect the networks.• No global control at the operations level.CS 213 S’01– 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 to a particular implementation of that idea (The global IP Internet).CS 213 S’01– 10 –class30.pptInternetworking with repeatersrrrrRepeaters (also called hubs)(r in the figure) directly transfer bits from their inputs to their outputsCS 213 S’01– 11 –class30.pptInternetworking with repeatersHost on network AHost on network BTelnet, FTP, HTTP, emailapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata link10Base-TphysicalRepeater(forwards bits)CS 213 S’01– 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 ethernet outlet.Cons• Not scalable–ethernet standard allows only 4 repeaters.–more than 4 would introduce delays that would break contention detection.• No heterogeneity–Networks connected with repeaters must have identical electricalproperties.CS 213 S’01– 13 –class30.pptInternetworking with bridgesbbbbBridges (b In the figure) maintain a cache of hosts on their input segments.Selectively transferethernet frames from their inputs to their outputs.CS 213 S’01– 14 –class30.pptInternetworking with bridgesHost on network AHost on network BTelnet, FTP, HTTP, emailapplicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkCSMA/CD10Base-TphysicalBridge(forwards ethernetframes)CS 213 S’01– 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 S’01– 16 –class30.pptInternetworking with routersDef: An internetwork (internet for short) is an arbitrary collection of physical networks interconnected by routers to provide some sort of host-to-host packet delivery service.internethosthosthosthostCS 213 S’01– 17 –class30.pptBuilding an internetXY Znetwork 2 (ECE)adapter adapteradapterAB Cnetwork 1 (SCS)adapter adapteradapterWe start with two separate, unconnected computer networks (subnets), which are at different locations, and possibly built by different vendors.Ethernet ATMQuestion: How to present the illusion of one network?CS 213 S’01– 18 –class30.pptBuilding an internet (cont)XY Znetwork 2 (ECE)adapter adapteradapterABC (router)network 1 (SCS)adapter adapteradapterNext we physically connect one of the computers, called a router(in this case computer C), to each of the networks.adapterCS 213 S’01– 19
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