Data Communication and NetworksA Communications ModelSimplified Communications Model - DiagramKey Communications TasksSimplified Data Communications ModelNetworkingSimplified Network ModelWide Area NetworksCircuit SwitchingPacket SwitchingFrame RelayAsynchronous Transfer ModeLocal Area NetworksProtocolsKey Elements of a ProtocolWhat’s a protocol?Slide 17In Summary, a protocol is ....Protocol SpecificationEvent -Time DiagramsTransition DiagramProtocol ArchitectureA Three Layer ModelNetwork Access LayerTransport LayerApplication LayerAddressing RequirementsProtocol Architectures and NetworksProtocols in Simplified ArchitectureStandardized Protocol ArchitecturesOSIOSI - The ModelOSI LayersTCP/IP Protocol ArchitecturePhysical LayerSlide 36Internet Layer (IP)Transport Layer (TCP)Slide 39TCP/IP Protocol Architecture ModelPDUs in TCP/IPOSI v TCP/IPStandardsData Communication and NetworksLecture 1Introduction and Overview September 8, 2005A Communications ModelSourcegenerates data to be transmittedTransmitterConverts data into transmittable signalsTransmission SystemCarries dataReceiverConverts received signal into dataDestinationTakes incoming dataSimplified Communications Model - DiagramKey Communications TasksTransmission System UtilizationInterfacingSignal GenerationSynchronizationError detection and correctionAddressing and routingRecoveryMessage formattingSecurityNetwork ManagementSimplified Data Communications ModelNetworkingPoint to point communication not usually practicalDevices are too far apartLarge set of devices would need impractical number of connectionsSolution is a communications networkSimplified Network ModelWide Area NetworksLarge geographical areaCrossing public rights of wayRely in part on common carrier circuitsAlternative technologiesCircuit switchingPacket switchingFrame relayAsynchronous Transfer Mode (ATM)Circuit SwitchingDedicated communications path established for the duration of the conversatione.g. telephone networkPacket SwitchingData sent out of sequenceSmall chunks (packets) of data at a timePackets passed from node to node between source and destinationUsed for terminal to computer and computer to computer communicationsFrame RelayPacket switching systems have large overheads to compensate for errorsModern systems are more reliableErrors can be caught in end systemMost overhead for error control is stripped outAsynchronous Transfer ModeATMEvolution of frame relayLittle overhead for error controlFixed packet (called cell) lengthAnything from 10Mbps to GbpsConstant data rate using packet switching techniqueLocal Area NetworksSmaller scopeBuilding or small campusUsually owned by same organization as attached devicesData rates much higherUsually broadcast systemsProtocolsUsed for communications between entities in a systemMust speak the same languageEntitiesUser applicationse-mail facilitiesterminalsSystemsComputerTerminalRemote sensorKey Elements of a ProtocolSyntaxData formatsSignal levelsSemanticsControl informationError handlingTimingSpeed matchingSequencingWhat’s a protocol?human protocols:“what’s the time?”“I have a question”introductions… specific msgs sent… specific actions taken when msgs received, or other eventsnetwork protocols:machines rather than humansall communication activity in Internet governed by protocolsprotocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt From Computer Networking: A Top-Down Approach Featuring the Internet by Kurose & RossWhat’s a protocol?a human protocol and a computer network protocol:HiHiGot thetime?2:00TCP connection req.TCP connectionreply.Get http://gaia.cs.umass.edu/index.htm<file>timeFrom Computer Networking: A Top-Down Approach Featuring the Internet by Kurose & RossIn Summary, a protocol is ....An agreement about communication between two or more entitiesIt specifies– Format of messages– Meaning of messages– Rules for exchange– Procedures for handling problemsProtocol SpecificationAs designers, we can specify a protocol usingSpace-Time DiagramsTransition DiagramsWe can implement a protocol with a Finite State Machine (FSM)Internet Protocols are formalized by RFCs which are administered by IETF01/14/19 20Event -Time Diagrams• Defines causal ordering• Defines indication/request/response actionsTransition DiagramIllustratesStatesInput (the event that causes transition)Transitions (to new states)Protocol ArchitectureTask of communication broken up into modulesFor example file transfer could use three modulesFile transfer applicationCommunication service moduleNetwork access moduleA Three Layer ModelNetwork Access LayerTransport LayerApplication LayerNetwork Access LayerExchange of data between the computer and the networkSending computer provides address of destinationMay invoke levels of serviceDependent on type of network used (LAN, packet switched etc.)Transport LayerReliable data exchangeIndependent of network being usedIndependent of applicationApplication LayerSupport for different user applicationse.g. e-mail, file transferAddressing RequirementsTwo levels of addressing requiredEach computer needs unique network addressEach application on a (multi-tasking) computer needs a unique address within the computerThe service access point or SAPThe port on TCP/IP stacksProtocol Architectures and NetworksProtocols in Simplified ArchitectureStandardized Protocol ArchitecturesRequired for devices to communicateVendors have more marketable productsCustomers can insist on standards based equipmentTwo standards:OSI Reference modelNever lived up to early promisesTCP/IP protocol suiteMost widely usedAlso: IBM Systems Network Architecture (SNA)OSIOpen Systems InterconnectionDeveloped by the International Organization for Standardization (ISO)Seven layersA theoretical system delivered too late!TCP/IP is the de facto standardOSI - The ModelA layer modelEach layer performs a subset of the required communication functionsEach layer relies on the next lower layer to perform more primitive functionsEach layer provides services to the next