Lect. 1: Oct 14, 2013Computer Networking Prof. Hanoch Levy (hanoch at cs.tau.ac.il) Teaching Assistant: Allon Wagner*

Lecture 1

Lect. 1: Oct 14, 2013Course InformationLectures: Wednesday 12 - 15 Dach 005Exercises: Monday 10 11, 11 12 Shenkar Physics 104Web site: http://www.cs.tau.ac.il/~allonwag/comnet2014A/index.html An Engineering Approach to Computer Networking / Keshav Computer Networks / Tanenbaum Data Networks / Bertsekas and GallagerA Top-down Approach to Computer Networking / Kurouse-Ross Books:*/71

Lect. 1: Oct 14, 2013Practical InformationHomework assignment: Mandatory Both theoretical and programming

Grades:Final Exam: 60% theory exercises: 20%Programming exercises: 20%*/71

Lect. 1: Oct 14, 2013MotivationTodays economymanufacturing, distributing, and retailing goodsbut also creating and disseminating informationpublishingbankingfilm making.part of the information economyFuture economy is likely to be dominated by information!*/71

Lect. 1: Oct 14, 2013Information?A representation of knowledgeExamples:booksbillsCDs & DVDsCan be represented in two waysanalog (waves/atoms)digital (bits)the Digital Revolutionconvert information as waves/atoms to info as bitsuse networks to move bits around instead of atoms */71

Lect. 1: Oct 14, 2013The Challengesrepresent all types of information as bits.move the bits In large quantities,everywhere, cheaply, Securely,with quality of service,.

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Lect. 1: Oct 14, 2013Todays Networks are complex!hostsrouterslinks of various mediaapplicationsprotocolshardware, software

Tomorrows will be even more! */71

Lect. 1: Oct 14, 2013*Internet Physical InfrastructureResidential accessCableFiberDSLWirelessCampus access, e.g.,EthernetWirelessThe Internet is a network of networksEach individually administrated network is called an Autonomous System (AS)*/71

Lecture 1

Lect. 1: Oct 14, 2013This 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

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Lect. 1: Oct 14, 2013Early 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. */71Circuit switching

Lect. 1: Oct 14, 2013Data Networksset of interconnected nodes exchange informationsharing of the transmission circuits= "switching".many links allow more than one path between every 2 nodes.network must select an appropriate path for each required connection.*/71

Lect. 1: Oct 14, 2013Qwest backbone http://www.qwest.com/largebusiness/enterprisesolutions/networkMaps/preloader.swf*/71

Lect. 1: Oct 14, 2013Networking Issues - TelephonyAddressing - identify the end userphone 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 senttelephone Samples @ Fixed sampling rate. not self descriptive! have to know where and when a sample came*/71

Lecture 1

Lect. 1: Oct 14, 2013Networking Issues - InternetAddressing - identify the end userIP addresses 132.66.48.37, 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).*/71

Lect. 1: Oct 14, 2013Telephone networks support a single, end-to-end quality of service but is expensive to bootInternet supports no quality of service but is flexible and cheapFuture networks will have to support a wide range of service qualities at a reasonable cost*/71

Lect. 1: Oct 14, 2013History 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*/71

Lect. 1: Oct 14, 2013History 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*/71

Lect. 1: Oct 14, 2013Cerf and Kahns internetworking principles:minimalism, autonomy - no internal changes required to interconnect networksbest effort service modelstateless routersdecentralized controlDefines todays Internet architecture*/71

Lect. 1: Oct 14, 2013History 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

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Lect. 1: Oct 14, 2013History 1990 - : commercialization and WWWearly 1990s: ARPAnet decommissioned1991: 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*/71

Lect. 1: Oct 14, 2013Demand and SupplyHuge growth in usersThe introduction of the webFaster home accessBetter user experience.InfrastructureSignificant portion of telecommunication.New evolving industriesAlthough, sometimes temporary setbacks*/71

Lect. 1: Oct 14, 2013Internet: Users */71

Lect. 1: Oct 14, 2013Penetration around the Globe (2009)http://www.internetworldstats.com/stats.htm*/71

Lect. 1: Oct 14, 2013Users around the Globe (2002/5/9)*/71

Lect. 1: Oct 14, 2013Technology: Modem speed*/71

Lect. 1: Oct 14, 2013Todays optionsModem: 56 KISDN: 64K 128KFrame Relay: 56K ++Today High Speed ConnectionsCable, ADSL, Satellite.All are available at 5Mb (2005)30 Mb (2009)OBSOLETE*/71

Lect. 1: Oct 14, 2013Coming soon (1999) */71

Lect. 1: Oct 14, 2013Today (2005)*/71

Lect. 1: Oct 14, 2013Why do we need StandardsNetworks (and other media) support communication between different entitiesNeed agreement to ensure correct, efficient and meaningful communication*/71

Lect. 1: Oct 14, 2013Various Organizations Issue StandardsIEEE (Institute for Electrical and Electronic Engineers)IETF (Internet Engineering Task Force)ITU (International Telecommunications Union)ISO (International Organization for Standardization)W3C (World Wide Web Consortium)*/71

Lect. 1: Oct 14, 2013Protocol LayersA way for organizing structure of networkThe idea: a series of steps Or at least our discussion of networks*/71

Lect. 1: Oct 14, 2013Protocol LayeringNecessary because communication is complexIntended primarily for protocol designersDivides the problem into intellectually manageable piecesProvides a conceptual framework that can help us understand protocolsThink of layering as a guideline, not a rigid specificationUnderstand that optimizations may violate strict layeringShould be invisible to users*/71Layering in protocols ~Functions in programs

Lect. 1: Oct 14, 2013Mail system functionality*/71

Lect. 1: Oct 14, 2013How do we Communicate?Send a mail from Alice to BobAlice in Champaign, Bob in HollywoodExample:US Postal ServiceBob

Champaign, Illinois

Hollywood, CaliforniaAlice*/71

Lect. 1: Oct 14, 2013What does Alice do?Bobs address (to a mailbox)Bobs name in case people share mailboxPostage have to pay!Alices own name and address in case Bob wants to return a messageIn case the mail has to be returned.Bob100 Santa Monica Blvd.Hollywood, CA 90028Alice200 Cornfield Rd.Champaign, IL 61820*/71

Lect. 1: Oct 14, 2013What does Bob do?Install a mailboxReceive the mailGet rid of envelopeRead the messageBob100 Santa Monica Blvd.Hollywood, CA 90028Alice200 Cornfield Rd.Champaign, IL 61820*/71

Lect. 1: Oct 14, 2013Layers: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 service via its own internal-layer actions / intra layer peering relying on services provided by layer belowPeer entities*/71

Lecture 1

Lect. 1: Oct 14, 2013Advantages 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 systemDisadvantage: low efficiency*/71

Lect. 1: Oct 14, 2013ProtocolsA protocol is a set of rules and formats that govern the communication between communicating peerset of valid messages - syntaxmeaning of each message semanticsNecessary for any function that requires cooperation between peers*/71e.g: Every car drives on the right

Lect. 1: Oct 14, 2013A 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 entityE.g, truck company (drivers) uses a protocol to present post offices with the abstraction of an unreliable parcel transfer serviceProtocols*/71

Lect. 1: Oct 14, 2013Protocol 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.*/71

Lect. 1: Oct 14, 2013Open 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*/71

Lect. 1: Oct 14, 2013ISO 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*/71

Lect. 1: Oct 14, 2013The seven LayersEnd systemEnd systemIntermediate systemThere are only 5 !!Application */71

Lect. 1: Oct 14, 2013The seven Layers - protocol stackdataDH+data+DTbitsTHNetworkData LinkPhysicalSession and presentation layers are not so important, and are often ignored*/71

Lect. 1: Oct 14, 2013 ApplicationTransportNetworkData-LinkApplicationTransportNetworkData-LinkNetworkIdentical messageIdentical messageIdentical messageSourceDestination X X */71

Lect. 1: Oct 14, 2013Postal 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.Transport layer: mail clerk sends a message, retransmits if not ackedNetwork layer: postal system computes a route and forwards the lettersdatalink layer: letters carried between intermediate stops (e.g connecting flights) physical layer: carrying the letter itself between intermediate stops (planes, trains, automobiles)*/71

hanoch - upto here 16/10 / 13

Lect. 1: Oct 14, 2013Internet 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*/71

Lect. 1: Oct 14, 2013applicationtransportnetworkLinkphysicalsourcedestinationmessagesegmentdatagramframeProtocol layering and data*/71

Lect. 1: Oct 14, 2013Physical layer L1Physically Moves 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.*/71

Lect. 1: Oct 14, 2013Datalink layer L2(Reliable) 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 Ethernet (+access)others are FDDI, SONET, HDLC*/71

Lect. 1: Oct 14, 2013Datalink 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 it need datalink-layer address also needs to decide who gets to speak next these functions are provided by Medium ACcess sublayer (MAC = layer 1.5)*/71An interesting story in evolution

Lect. 1: Oct 14, 2013Network layer L3Carries 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*/71

Lect. 1: Oct 14, 2013Network layer typesIn 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)*/71

Lect. 1: Oct 14, 2013Internetnetwork layer is provided by Internet Protocol (IP)found 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.)*/71

Lect. 1: Oct 14, 2013At intermediate systemsparticipates in routing protocol to create routing tablesresponsible for forwarding packetsschedules the transmission order of packetschooses which packets to dropNetwork layer (contd.) At end-systems primarily hides details of datalink layer segments and reassemble detects errors*/71

Lect. 1: Oct 14, 2013Transport layer L4Reliable 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*/71

Lect. 1: Oct 14, 2013Transport 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*/71

Lect. 1: Oct 14, 2013Session layerNot commonProvides full-duplex service, expedited data delivery, and session synchronizationInternetdoesnt have a standard session layer

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Lect. 1: Oct 14, 2013Duplexif 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

Session layer (cont.)*/71

Lect. 1: Oct 14, 2013Presentation 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*/71

Lect. 1: Oct 14, 2013Application layerThe set of applications that use the networkDoesnt provide services to any other layer*/71

Lect. 1: Oct 14, 2013 VoIPUDPNetwork (IPv4)EthernetApplicationTransportNetworkData-LinkNetworkSourceDestinationEmail(smtp)ftpTCPWiFiModem*/71

Lect. 1: Oct 14, 2013 NetworkSourceDestinationapp1UDPNetwork (IPv4)Ethernetapp2app3TCPWiFiModem*/71

Lect. 1: Oct 14, 2013DiscussionLayers 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

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Lect. 1: Oct 14, 2013Course outline*

***************************Slide from 1999******************2nd break ?!***************