Computer networks--networks

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Transcript of Computer networks--networks

  • 1. Computer Networking1

2. 2!Todays Networks are complexhostsrouterslinks of various mediaapplicationsprotocolshardware, softwareTomorrows will be even more! 3. 3Early communicationssystems I.e. telephone point-to-point links directly connect together the users wishing tocommunicate use dedicated communication circuit if distance between users increases beyond thelength of the cable, the connection is formed by anumber of sections connected end-to-end in series. 4. 4Data Networks set of interconnected nodes exchange information sharing of the transmission circuits= "switching". many links allow more than one path between every2 nodes. network must select an appropriate path for eachrequired connection. 5. 5Networking Issues - TelephoneAddressing - identify the end userphone number 359 52 359524 = country code + city code +exchange + number Routing - How to get from source to destination.Telephone circuit switching: Based on the phone number. Information Units - How is information sent 6. 6Networking Issues - InternetAddressing - identify the end userIP addresses, Refer to a host interface =network number + host numberRouting- How to get from source to destinationPacket switching: move packets (chunks) of data amongrouters from source to destination independently.Information Units - How is information sent.Self-descriptive data: packet = data + metadata (header). 7. 7Telephone networks support a single, end-to-endquality of service but is expensive to bootInternet supports no quality of service but isflexible and cheapFuture networks will have to support a widerange of service qualities at a reasonable cost 8. 8History1961-1972: Early packet-switching principles1961: Kleinrock - queuing theory shows effectiveness ofpacket-switching1964: Baran - packet-switching in military networks1967: ARPAnet conceived by Advanced ResearchProjects Agency1969: first ARPAnet node operational1972: ARPAnet demonstrated publicly NCP (Network Control Protocol) first host-hostprotocol first e-mail program ARPAnet has 15 nodes 9. 9History1972-1980: Internetworking, new andproprietary nets1970: ALOHAnet satellite network in Hawaii1973: Metcalfes PhD thesis proposes Ethernet1974: Cerf and Kahn - architecture for interconnectingnetworkslate70s: proprietary architectures: DECnet, SNA, XNAlate 70s: switching fixed length packets (ATM precursor)1979: ARPAnet has 200 nodes 10. 10Cerf and Kahns : internetworking principles minimalism, autonomy - no internalchanges required to interconnect networks best effort service model stateless routers decentralized controlDefines todays Internet architecture 11. 11History1980-1990: new protocols,proliferation of networks1983: deployment of TCP/IP1982: SMTP e-mail protocol defined1983: DNS defined for name-to-IP-address translation1985: FTP protocol defined1988: TCP congestion controlnew national networks: CSnet, BITnet, NSFnet, Minitel100,000 hosts connected to confederation of networks 12. 12History1990 - : commercialization and WWWearly 1990s: ARPAnet decomissioned1991: NSF lifts restrictions on commercial use ofNSFnet (decommissioned, 1995)early 1990s: WWWhypertext [Bush 1945, Nelson 1960s]HTML, http: Berners-Lee1994: Mosaic, later Netscapelate 1990s: commercialization of WWW2004-2005: Web 2.0 (OReilly) 13. 13Demand and Supply Huge growth in users The introduction of the web Faster home access Better user experience. Infrastructure Significant portion of telecommunication. New evolving industries Although, sometimes temporary setbacks 14. 14Internet: Users10009008007006005004003002001000Million users1992 1996 2000 2001 2002 2003 2004 2005 2006 2007 2009year 15. Users around ( the Globe (2002/817AfricaEuropeLatinAmericaAustraliaMiddleEastUSACanadaAsiaPacific350300250200150100500AfricaAsia/PacificEuropeMiddle EastUSA+CanadaLatin AmericaAustralia20052002 16. 18Protocol Layers A way for organizing structure of network Or at least our discussion of networks The idea: a series of steps 17. 19Advantages of Layering explicit structure allows identification &relationship of complex systems pieces layered reference model for discussion modularization eases maintenance &updating of system change of implementation of layersservice transparent to rest of system 18. 20Protocols A protocol is a set of rules and formatsthat govern the communication betweencommunicating peers set of valid messages meaning of each message Necessary for any function that requirescooperation between peers 19. 21Protocols A protocol provides a service For example: the post office protocol for reliableparcel transfer service Peer entities use a protocol to provide aservice to a higher-level peer entity for example, truck drivers use a protocol topresent post offices with the abstraction of anunreliable parcel transfer service 20. 22Protocol Layers A network that provides many services needsmany protocols Some services are independent, But othersdepend on each other A Protocol may use another protocol as a step inits execution for example, ground transfer is one step in theexecution of the example reliable parcel transferprotocol This form of dependency is called layering Post office handling is layered above parcel groundtransfer protocol. 21. 23Open protocols and systems A set of protocols is open if protocol details are publicly available changes are managed by an organization whosemembership and transactions are open to the public A system that implements open protocols iscalled an open system International Organization for Standards (ISO)prescribes a standard to connect open systems open system interconnect (OSI) Has greatly influenced thinking on protocolstacks 22. 24ISO OSI reference model Reference model formally defines what is meant by a layer, a serviceetc. Service architecture describes the services provided by each layer andthe service access point Protocol architecture set of protocols that implement the servicearchitecture compliant service architectures may still use non-compliantprotocol architectures 23. 25The seven LayersApplicationPresentationSessionTransportNetworkData LinkPhysicalApplicationPresentationSessionTransportNetworkData LinkPhysicalNetworkData LinkPhysicalEnd system Intermediate End systemsystem 24. 26The seven Layers - protocol stackApplicationPresentationSessionTransportNetworkData LinkPhysicalApplicationPresentationSessionTransportNetworkData LinkPhysicaldatadatadatadataDH+data+DTbitsdataAHPHSHTHNetworkData LinkPhysicalNH dataSession and presentation layers are not so important, and are often ignored 25. 27Postal network Application: people using the postal system Session and presentation: chief clerk sends somepriority mail, and some by regular mail ; translatortranslates letters going abroad. mail clerk sends a message, retransmits if not acked postal system computes a route and forwards theletters datalink layer: letters carried by planes, trains,automobiles physical layer: the letter itself 26. 28Internet protocol stack application: supporting network applications ftp, smtp, http transport: host-host data transfer tcp, udp network: routing of datagrams from sourceto destination ip, routing protocols link: data transfer between neighboringnetwork elements ppp, ethernet physical: bits on the wireapplicationtransportnetworklinkphysical 27. 29source destinationapplicationtransportnetworkLinkphysicalapplicationtransportnetworkLinkphysicalMMMMHtHnHtHl HnHtMMMMHtHnHtHl HnHtmessagesegmentdatagramframeProtocol layering and data 28. 30Physical layer Moves bits between physically connectedend-systems Standard prescribes coding scheme to represent a bit shapes and sizes of connectors bit-level synchronization Internet technology to move bits on a wire, wireless link, satellitechannel etc. 29. 31Datalink layer (Reliable) communication over a singlelink. Introduces the notion of a frame set of bits that belong together Idle markers tell us that a link is not carrying aframe Begin and end markers delimit a frame Internet a variety of datalink layer protocols most common is Ethernet others are FDDI, SONET, HDLC 30. end-system must receive only bits meant for itneed datalink-layer addressalso need to decide who gets to speak nextthese functions are provided by Medium ACcess sublayer (MAC)32.(Datalink layer (contd Ethernet (broadcast link) Datalink layer protocols are the first layer of software Very dependent on underlying physical link properties Usually bundle both physical and datalink in hardware. 31. 33Network layer Carries data from source to destination. Logically concatenates a set of links to form theabstraction of an end-to-end link Allows an end-system to communicate with any otherend-system by computing a route between them Hides idiosyncrasies of datalink layer Provides unique network-wide addresses Found both in end-systems and in intermediate systems 32. 34Network layer types In datagram networks provides both routing and data forwarding In connection-oriented network separate data plane and control plane data plane only forwards and schedules data(touches every byte) control plane responsible for routing, call-establishment,call-teardown (doesnt touch databytes) 33. 35.(Network layer (contd Internet network layer is provided by Internet Protocol (IP) found in all end-systems and intermediate systems provides abstraction of end-to-end link segmentation and reassembly packet-forwarding, routing, scheduling unique IP addresses can be layered over anything, but only best-effortservice 34. 36.(Network layer (contd At end-systems primarily hides details of datalink layer segments and reassemble detects errors At intermediate systems participates in routing protocol to create routingtables responsible for forwarding packets schedules the transmission order of packets chooses which packets to drop 35. 37Transport layer Reliable end-to-end communication. creates the abstraction of an error-controlled,flow-controlled and multiplexed end-to-end link(Network layer provides only a raw end-to-end service) Some transport layers provide fewer services e.g. simple error detection, no flow control, and no retransmission InternetTCP provides error control, flow control, multiplexingUDP provides only multiplexing 36. 38.(Transport layer (contd Error control GOAL: message will reach destination despite packet loss,corruption and duplication ACTIONS: retransmit lost packets; detect, discard, andretransmit corrupted packets; detect and discard duplicatedpackets Flow control match transmission rate to rate currently sustainable on the pathto destination, and at the destination itself Multiplexes multiple applications to the sameend-to-end connection adds an application-specific identifier (port number) so thatreceiving end-system can hand in incoming packet to the correctapplication 37. 39Session layer Not common Provides full-duplex service, expedited datadelivery, and session synchronization Internet doesnt have a standard session layer 38. 40.(Session layer (cont Duplex if transport layer is simplex, concatenates two transportendpoints together Expedited data delivery allows some messages to skip ahead in end-systemqueues, by using a separate low-delay transport layerendpoint Synchronization allows users to place marks in data stream and to roll backto a prespecified mark 39. 41Presentation layer Usually ad hoc Touches the application data(Unlike other layers which deal with headers) Hides data representation differences betweenapplications characters (ASCII, unicode, EBCDIC.) Can also encrypt data Internet no standard presentation layer only defines network byte order for 2- and 4-byteintegers 40. 42Application layer The set of applications that use the network Doesnt provide services to any other layer