Page 1InternetworkingNovember 9, 2007InternetworkingNovember 9, 2007TopicsTopics Client-server programming model Networks Internetworks Global IP Internetz IP addressesz Domain namesz Connections15-213“The course that gives CMU its Zip!”lecture-21.ppt–2–15-213, F’07A Client-Server TransactionA Client-Server TransactionClientprocessServerprocess1. Client sends request2. Server handlesrequest3. Server sends response4. Client handlesresponseResourceMost network applications are based on the clientMost network applications are based on the client--server server model:model: A server process and one or more client processes Server manages some resource. Server provides service by manipulating resource for clients Server activated by request from client (vending machine analogy)Note: clients and servers are processes running on hosts (can be the same or different hosts).–3–15-213, F’07Computer NetworksComputer NetworksA network is a hierarchical system of boxes and wires A network is a hierarchical system of boxes and wires organized by geographical proximityorganized by geographical proximity SAN (System Area Network) spans cluster or machine roomSwitched 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 An internetworkinternetwork((internetinternet) ) is an interconnected set of is an interconnected set of networks.networks. The Gobal IP Internet (uppercase “I”) is the most famous example of an internet (lowercase “i”)LetLet’’s see how we would build an internet from the s see how we would build an internet from the ground up.ground up.–4–15-213, F’07Lowest Level: Ethernet SegmentLowest Level: Ethernet SegmentEthernet segment consists of a collection of Ethernet segment consists of a collection of hostshostsconnected by connected by wires (twisted pairs) to a wires (twisted pairs) to a hubhub. . Spans room or floor in a building.Spans room or floor in a building.OperationOperation 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.Note: Hubs are on their way out. Bridges (switches, routers) became cheap enough to replace them (means no more broadcasting)hosthost hosthub100 Mb/s100 Mb/sports–5–15-213, F’07Next Level: Bridged Ethernet SegmentNext Level: Bridged Ethernet SegmentSpans building or campus.Spans building or campus.Bridges cleverly learn which hosts are reachable from which portBridges cleverly learn which hosts are reachable from which ports s and then selectively copy frames from port to port.and then selectively copy frames from port to port.hosthost host host hosthub hubbridge100 Mb/s100 Mb/shosthosthub100 Mb/s 100 Mb/s1 Gb/shosthost hostbridgehosthosthubABCXY–6–15-213, F’07Conceptual View of LANsConceptual View of LANsFor simplicity, hubs, bridges, and wires are often shown as a For simplicity, hubs, bridges, and wires are often shown as a collection of hosts attached to a single wire:collection of hosts attached to a single wire:hosthost host...Page 2–7–15-213, F’07Next Level: internetsNext Level: internetsMultiple incompatible LANs can be physically connected by Multiple incompatible LANs can be physically connected by specialized computers called specialized computers called routersrouters..The connected networks are called an The connected networks are called an internetinternet..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 Wifi, 802.11*, T1-links, DSL, …)–8–15-213, F’07Logical structure of an internetLogical structure of an internet Ad hoc interconnection of networksz No particular topologyz Vastly different router & link capacities Send packets from source to destination by hopping through networksz Router forms bridge from one network to anotherz Different packets may take different routeshosthostrouterrouterrouterrouterrouterrouter–9–15-213, F’07The Notion of an internet ProtocolThe Notion of an internet ProtocolHow is it possible to send bits across incompatible How is it possible to send bits across incompatible LANs and WANs?LANs and WANs?Solution: protocol software running on each host and Solution: protocol software running on each host and router router smoothssmoothsout the differences between the out the differences between the different networks.different networks.Implements an internet protocol (i.e., set of rules) that Implements an internet protocol (i.e., set of rules) that governs how hosts and routers should cooperate governs how hosts and routers should cooperate when they transfer data from network to network.when they transfer data from network to network. TCP/IP is the protocol for the global IP Internet.–10–15-213, F’07What Does an internet Protocol Do?What Does an internet Protocol Do?1. Provides a naming scheme1. 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 identifies it.2. Provides a delivery mechanism2. Provides a delivery mechanism An internet protocol defines a standard transfer unit (packet) Packet consists of header and payloadz Header: contains info such as packet size, source and destination addresses.z Payload: contains data bits sent from source host.–11–15-213, F’07Transferring Data Over an internetTransferring Data Over an internetprotocolsoftwareclientLAN1adapterHost ALAN1LAN2data(1)data PH FH1(4)data PH FH2(6)data(8)data PH FH2(5)LAN2 frameprotocolsoftwareLAN1adapterLAN2adapterRouterdata PH(3)FH1data PH FH1(2)internet packetLAN1 frame(7)data PH FH2protocolsoftwareserverLAN2adapterHost B–12–15-213, F’07Source: Boardwatch.comMCI/WorldCom/UUNET Global BackbonePage 3–13–15-213, F’07Other IssuesOther IssuesWe are glossing over a number of important questions:We 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
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