Internetworking Nov 20, 2001Topics• internets• The Global IP Internet• Programmer’s view of the Internetclass25.ppt15-213“The course that gives CMU its Zip!”CS 213 F’01– 2 –class25.pptA client-server transactionclientprocessserverprocess1. client sends request2. server handlesrequest3. server sends response4. client handlesresponseresourceEvery network application is based on the client-servermodel:• a server process and one or more client processes• server manages some resource.• server provides service by manipulating resource for clients.Note: clients and servers are processes running on hosts (can be the same or different hosts).CS 213 F’01– 3 –class25.pptHardware organization of a network hostmainmemoryI/O bridgeMIALUregister fileCPU chipsystem bus memory busdisk controllergraphicsadapterUSBcontrollermousekeyboard monitordiskI/O busExpansion slotsnetworkadapternetworkCS 213 F’01– 4 –class25.pptComputer networksA network is a hierarchical system of boxes and wiresorganized by geographical proximity• 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 ofnetworks.• The IP Internet is the most famous example of an internetwork.Let’s see how we would build an internetwork from theground up.CS 213 F’01– 5 –class25.pptLowest level: Ethernet segmentEthernet segment consists of a collection of hostsconnected by wires (twisted pairs) to a hub.Spans room or floor in a building.Operation• Each Ethernet adapter has a unique 48-bit address.• 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.hosthost hosthub100 Mb/s100 Mb/sportsCS 213 F’01– 6 –class25.pptNext level: Bridged Ethernet segmentSpans building or campus.Bridges cleverly learn which hosts are reachable fromwhich ports and then selectively copy frames fromport to port.hosthost host host hosthub hubbridge100 Mb/s100 Mb/shosthosthub100 Mb/s 100 Mb/s1 Gb/shosthost hostbridgehosthosthubA BCXYCS 213 F’01– 7 –class25.pptConceptual view of LANsFor simplicity, hubs, bridges, and wires are oftenshown as a collection of hosts attached to a singlewire:hosthost host...CS 213 F’01– 8 –class25.pptNext level: internetsMultiple incompatible LANs can be physicallyconnected by specialized computers called routers.The connected networks are called an internet.hosthost hostLAN 1...hosthost hostLAN 2...router router routerWAN WANLAN 1 and LAN 2 might be completely different,totally incompatible LANs (e.g., Ethernet and ATM)CS 213 F’01– 9 –class25.pptThe notion of an internet protocolHow is it possible to send bits across incompatibleLANs and WANs?Solution: protocol software running on each host androuter smooths out the differences between thedifferent networks.Implements an internet protocol (i.e., set of rules) thatgoverns how hosts and routers should cooperatewhen they transfer data from network to network.• TCP/IP is the protocol for the global IP Internet.CS 213 F’01– 10 –class25.pptWhat does an internet protocol do?Naming scheme• The internet protocol defines a uniform format for host addresses.• Each host (and router) is assigned at least one of these internetaddresses that uniquely identifies it.Delivery mechanism• The internet protocol defines a standard transfer unit (packet)• Packet consists of header and payload–header: contains info such as packet size, source and destinationaddresses.–payload: contains data bits sent from source host.CS 213 F’01– 11 –class25.pptTransferring data over an internetprotocolsoftwareclientLAN1adapterHost Adatadata PH FH1data PHdata PH FH2LAN1LAN2datadata PHFH1data PH FH2(1)(2)(3)(4)(5)(6)(7)(8)internet packetLAN2 frameprotocolsoftwareLAN1adapterLAN2adapterRouterFH1LAN1 framedata PH FH2protocolsoftwareserverLAN2adapterHost BCS 213 F’01– 12 –class25.pptOther issuesWe are glossing over a number of important questions:• What if different networks have different maximum frame sizes?(segmentation)• How do routers know where to forward frames?• How are routers informed when the network topology changes?• What if packets get lost?These questions form the heart of the area of computersystems known as networking.CS 213 F’01– 13 –class25.pptGlobal IP InternetMost famous example of an internet.Based on the TCP/IP protocol family.–IP (Internet protocol) :»provides basic naming scheme and unreliable deliverycapability of packets (datagrams) from host-to-host.–UDP (Unreliable Datagram Protocol)»uses IP to provide unreliable datagram delivery from process-to-process.–TCP (Transmission Control Protocol)»uses IP to provide reliable byte streams (like files) fromprocess-to-process.Accessed via a mix of Unix file I/O and functions fromthe Berkeley sockets interface.CS 213 F’01– 14 –class25.pptHardware and software organization of an Internet applicationTCP/IPclientnetworkadapterGlobal IP InternetTCP/IPservernetworkadapterInternet client host Internet server hostsockets interface(system calls)hardware interface(interrupts)user codekernel codehardwareCS 213 F’01– 15 –class25.pptBasic Internet componentsAn Internet backbone is a collection of routers(nationwide or worldwide) connected by high-speed point-to-point networks.A Network Access Point (NAP) is a router thatconnects multiple backbones (sometimesreferred to as peers).Regional networks are smaller backbones thatcover smaller geographical areas (e.g., citiesor states)A point of presence (POP) is a machine that isconnected to the Internet.Internet Service Providers (ISPs) provide dial-up or direct access to POPs.CS 213 F’01– 16 –class25.pptThe Internet circa 1993In 1993, the Internet consisted of one backbone(NSFNET) that connected 13 sites via 45 MbsT3 links.• Merit (Univ of Mich), NCSA (Illinois), Cornell TheoryCenter, Pittsburgh Supercomputing Center, San DiegoSupercomputing Center, John von Neumann Center(Princeton), BARRNet (Palo Alto), MidNet (Lincoln, NE),WestNet (Salt Lake City), NorthwestNet (Seattle),SESQUINET (Rice), SURANET (Georgia Tech).Connecting to the Internet involved connectingone of your routers to a router at a backbonesite, or to a regional network that was alreadyconnected to the backbone.CS 213 F’01– 17
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