Presentation about computer networking

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  • Computer Networking

    Yishay Mansour ( Nir Andelman (

  • Course InformationLectures: Tuesday 9-12Exercises: Wendsday 10-11Web site: Engineering Approach to Computer Networking / Keshav Computer Networks / Tanenbaum Data Networks / Bertsekas and GallagerA Top-down Approach to Computer Networking / Kurouse-Ross Books:

  • Practical Information

    Homework assignment: Mandatory Both theoretical and programming Done in pairs Grades:Final Exam: 60% February 5 and October 18theory exercises: 20%Programming exercises: 20%

  • MotivationTodays economymanufacturing, distributing, and retailing goodsbut also creating and disseminating informationpublishingbankingfilm making.

    part of the information economyFuture economy is likely to be dominated by information!

  • Information?A representation of knowledgeExamples:booksbillsCDsCan be represented in two waysanalog (atoms)digital (bits)the Digital Revolutionconvert information as atoms to information as bitsuse networks to move bits around instead of atoms

  • The Challengesrepresent all types of information as bits.move the bits In large quantities,everywhere, cheaply, Securely,with quality of service,.

  • Todays Networks are complex!hostsrouterslinks of various mediaapplicationsprotocolshardware, softwareTomorrows will be even more!

  • This courses ChallengeTo discuss this complexity in an organized way, that will make todays computer networks (and their limitations) more comprehensive.identification, and understanding relationship of complex systems pieces.Problems that are beyond a specific technology

  • Early communications systemsI.e. telephonepoint-to-point links directly connect together the users wishing to communicate use dedicated communication circuitif distance between users increases beyond the length of the cable, the connection is formed by a number of sections connected end-to-end in series.

  • Data Networksset of interconnected nodes exchange informationsharing of the transmission circuits= "switching".many links allow more than one path between every 2 must select an appropriate path for each required connection.

  • Networking Issues - TelephoneAddressing - identify the end user

    phone number 1-201-222-2673 = 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

    telephone Samples @ Fixed sampling rate. not self descriptive! have to know where and when a sample came

  • Networking Issues - InternetAddressing - identify the end userIP addresses, Refer to a host interface = network number + host number Routing- How to get from source to destinationPacket switching: move packets (chunks) of data among routers from source to destination independently. Information Units - How is information sent.Self-descriptive data: packet = data + metadata (header).

  • Telephone networks support a single, end-to-end quality of service but is expensive to bootInternet supports no quality of service but is flexible and cheapA future network will have to support a range of service qualities at a reasonable cost

  • History 1961-1972: Early packet-switching principles1961: Kleinrock - queuing theory shows effectiveness of packet-switching1964: Baran - packet-switching in military networks1967: ARPAnet conceived by Advanced Research Projects Agency1969: first ARPAnet node operational1972: ARPAnet demonstrated publiclyNCP (Network Control Protocol) first host-host protocol first e-mail programARPAnet has 15 nodes

  • History 1972-1980: Internetworking, new and proprietary nets1970: ALOHAnet satellite network in Hawaii1973: Metcalfes PhD thesis proposes Ethernet1974: Cerf and Kahn - architecture for interconnecting networkslate70s: proprietary architectures: DECnet, SNA, XNAlate 70s: switching fixed length packets (ATM precursor)1979: ARPAnet has 200 nodes

  • Cerf and Kahns internetworking principles:minimalism, autonomy - no internal changes required to interconnect networksbest effort service modelstateless routersdecentralized control

    Defines todays Internet architecture

  • History 1980-1990: new protocols, proliferation of networks1983: deployment of TCP/IP1982: SMTP e-mail protocol defined 1983: 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

  • History 1990 - : commercialization and WWWearly 1990s: ARPAnet decomissioned1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)early 1990s: WWWhypertext [Bush 1945, Nelson 1960s]HTML, http: Berners-Lee1994: Mosaic, later Netscapelate 1990s: commercialization of WWW

  • Demand and SupplyHuge growth in usersThe introduction of the webFaster home accessBetter user experience.InfrastructureSignificant portion of telecommunication.New evolving industriesAlthough, sometimes temporary setbacks

  • Internet: Users

  • Users around the Globe (2002)

  • Users around the Globe (2005)

  • Users around the Globe (2005)

  • Technology: Modem speed

  • Todays optionsModem: 56 KISDN: 64K 128KFrame Relay: 56K ++Today High Speed ConnectionsAll are available at 5Mb (2005)Cable, ADSL, Satellite.

  • Coming soon:

  • Today

  • Protocol LayersThe idea: a series of steps

    A way for organizing structure of network

    Or at least our discussion of networks

  • JFKTransportHandlingRouting

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  • Layers:Person delivery of parcel

    Post office counter handling

    Ground transfer: loading on trucks

    Airport transfer: loading on airplane

    Airplane routing from source to destination

    each layer implements a servicevia its own internal-layer actionsrelying on services provided by layer below

    Peer entities

  • Advantages of Layeringexplicit structure allows identification & relationship of complex systems pieceslayered reference model for discussionmodularization eases maintenance & updating of systemchange of implementation of layers service transparent to rest of system

  • Protocols

    A protocol is a set of rules and formats that govern the communication between communicating peersset of valid messagesmeaning of each message

    Necessary for any function that requires cooperation between peers

  • ProtocolsA protocol provides a serviceFor example: the post office protocol for reliable parcel transfer service

    Peer entities use a protocol to provide a service to a higher-level peer entityfor example, truck drivers use a protocol to present post offices with the abstraction of an unreliable parcel transfer service

  • Protocol LayersA network that provides many services needs many protocolsSome services are independent, But others depend on each otherA Protocol may use another protocol as a step in its executionfor example, ground transfer is one step in the execution of the example reliable parcel transfer protocolThis form of dependency is called layeringPost office handling is layered above parcel ground transfer protocol.

  • Open protocols and systemsA set of protocols is open ifprotocol details are publicly availablechanges are managed by an organization whose membership and transactions are open to the publicA system that implements open protocols is called an open systemInternational Organization for Standards (ISO) prescribes a standard to connect open systemsopen system interconnect (OSI) Has greatly influenced thinking on protocol stacks

  • ISO OSI reference modelReference modelformally defines what is meant by a layer, a service etc.Service architecturedescribes the services provided by each layer and the service access point Protocol architectureset of protocols that implement the service architecturecompliant service architectures may still use non-compliant protocol architectures

  • The seven LayersEnd systemEnd systemIntermediate system

  • The seven Layers - protocol stackdataDH+data+DTbitsTHNetworkData LinkPhysicalSession and presentation layers are not so important, and are often ignored

  • Postal network

    Application: people using the postal systemSession and presentation: chief clerk sends some priority mail, and some by regular mail ; translator translates letters going abroad.mail clerk sends a message, retransmits if not ackedpostal system computes a route and forwards the lettersdatalink layer: letters carried by planes, trains, automobilesphysical layer: the letter itself

  • Internet protocol stackapplication: supporting network applicationsftp, smtp, httptransport: host-host data transfertcp, udpnetwork: routing of datagrams from source to destinationip, routing protocolslink: data transfer between neighboring network elementsppp, ethernetphysical: bits on the wire

  • Protocol layering and dataapplicationtransportnetworkLinkphysicalsourcedestinationmessagesegmentdatagramframe

  • Physical layerMoves bits between physically connected end-systemsStandard prescribescoding scheme to represent a bitshapes and sizes of connectorsbit-level synchronizationInternettechnology to move bits on a wire, wireless link, satellite channel etc.

  • Datalink layerReliable communication over a single link.Introduces the notion of a frameset of bits that belong togetherIdle markers tell us that a link is not carrying a frameBegin and end markers delimit a frameInterneta variety of datalink layer protocolsmost common is Ethernetothers are FDDI, SONET, HDLC

  • Datalink layer (contd.)Datalink layer protocols are the first layer of softwareVery dependent on underlying physical link propertiesUsually bundle both physical and datalink in hardware.

    Ethernet (broadcast link) 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)

  • Network layerCarries data from source to destination.Logically concatenates a set of links to form the abstraction of an end-to-end linkAllows an end-system to communicate with any other end-system by computing a route between themHides idiosyncrasies of datalink layerProvides unique network-wide addressesFound both in end-systems and in intermediate systems

  • Network layer types

    In datagram networksprovides both routing and data forwardingIn connection-oriented network separate data plane and control planedata plane only forwards and schedules data (touches every byte)control plane responsible for routing, call-establishment, call-teardown (doesnt touch data bytes)

  • Network layer (contd.)

    Internetnetwork layer is provided by Internet Protocolfound in all end-systems and intermediate systemsprovides abstraction of end-to-end linksegmentation and reassemblypacket-forwarding, routing, schedulingunique IP addressescan be layered over anything, but only best-effort service

  • Network layer (contd.)At intermediate systemsparticipates in routing protocol to create routing tablesresponsible for forwarding packetsschedules the transmission order of packetschooses which packets to drop

    At end-systems primarily hides details of datalink layer segments and reassemble detects errors

  • Transport layerReliable 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 servicese.g. simple error detection, no flow control, and no retransmission

    Internet TCP provides error control, flow control, multiplexingUDP provides only multiplexing

  • Transport layer (contd.)Error controlGOAL: message will reach destination despite packet loss, corruption and duplicationACTIONS: retransmit lost packets; detect, discard, and retransmit corrupted packets; detect and discard duplicated packetsFlow controlmatch transmission rate to rate currently sustainable on the path to destination, and at the destination itselfMultiplexes multiple applications to the same end-to-end connectionadds an application-specific identifier (port number) so that receiving end-system can hand in incoming packet to the correct application

  • Session layerNot commonProvides full-duplex service, expedited data delivery, and session synchronizationInternetdoesnt have a standard session layer

  • Session layer (cont.)Duplexif transport layer is simplex, concatenates two transport endpoints togetherExpedited data deliveryallows some messages to skip ahead in end-system queues, by using a separate low-delay transport layer endpointSynchronizationallows users to place marks in data stream and to roll back to a prespecified mark

  • Presentation layerUsually ad hocTouches the application data

    (Unlike other layers which deal with headers)Hides data representation differences between applicationscharacters (ASCII, unicode, EBCDIC.)Can also encrypt dataInternetno standard presentation layeronly defines network byte order for 2- and 4-byte integers

  • Application layerThe set of applications that use the networkDoesnt provide services to any other layer

  • DiscussionLayers break a complex problem into smaller, simpler pieces.Why seven layers?Need a top and a bottom 2Need to hide physical link; so need datalink 3Need both end-to-end and hop-by-hop actions; so need at least the network and transport layers 5

  • Course outline

    1Introduction and Layering2Data Link: Multi Access3Hubs, Bridges and Routers4Scheduling and Buffer Management5Switching Fabrics6Routing7Reliable Data Transfer8End to End Window Based Protocols9Flow Control10Multimedia and QoS11Network Security12Distributed Algorithms