(protocols and architecture (chapter 2
اسلاید 1: William Stallings Data and Computer CommunicationsChapter 2Protocols and Architecture
اسلاید 2: CharacteristicsDirect or indirectMonolithic or structuredSymmetric or asymmetricStandard or nonstandard
اسلاید 3: Direct or IndirectDirectSystems share a point to point link orSystems share a multi-point linkData can pass without intervening active agentIndirectSwitched networks orInternetworks or internetsData transfer depend on other entities
اسلاید 4: Monolithic or StructuredCommunications is a complex taskTo complex for single unitStructured design breaks down problem into smaller unitsLayered structure
اسلاید 5: Symmetric or AsymmetricSymmetricCommunication between peer entitiesAsymmetricClient/server
اسلاید 6: Standard or NonstandardNonstandard protocols built for specific computers and tasksK sources and L receivers leads to K*L protocols and 2*K*L implementationsIf common protocol used, K + L implementations needed
اسلاید 7: Use of Standard Protocols
اسلاید 8: FunctionsEncapsulationSegmentation and reassmeblyConnection controlOrdered deliveryFlow controlError controlAddressingMultiplexingTransmission services
اسلاید 9: EncapsulationAddition of control information to dataAddress informationError-detecting codeProtocol control
اسلاید 10: Segmentation (Fragmentation)Data blocks are of bounded sizeApplication layer messages may be largeNetwork packets may be smallerSplitting larger blocks into smaller ones is segmentation (or fragmentation in TCP/IP)ATM blocks (cells) are 53 octets longEthernet blocks (frames) are up to 1526 octets longCheckpoints and restart/recovery
اسلاید 11: Why Fragment?AdvantagesMore efficient error controlMore equitable access to network facilitiesShorter delaysSmaller buffers neededDisadvantagesOverheadsIncreased interrupts at receiverMore processing time
اسلاید 12: Connection ControlConnection EstablishmentData transferConnection terminationMay be connection interruption and recoverySequence numbers used for Ordered deliveryFlow controlError control
اسلاید 13: Connection Oriented Data Transfer
اسلاید 14: Ordered DeliveryPDUs may traverse different paths through networkPDUs may arrive out of orderSequentially number PDUs to allow for ordering
اسلاید 15: Flow ControlDone by receiving entityLimit amount or rate of data Stop and waitCredit systemsSliding windowNeeded at application as well as network layers
اسلاید 16: Error ControlGuard against loss or damageError detectionSender inserts error detecting bitsReceiver checks these bitsIf OK, acknowledgeIf error, discard packetRetransmissionIf no acknowledge in given time, re-transmitPerformed at various levels
اسلاید 17: AddressingAddressing levelAddressing scopeConnection identifiersAddressing mode
اسلاید 18: Addressing levelLevel in architecture at which entity is namedUnique address for each end system (computer) and routerNetwork level address IP or internet address (TCP/IP)Network service access point or NSAP (OSI)Process within the systemPort number (TCP/IP)Service access point or SAP (OSI)
اسلاید 19: Address Concepts
اسلاید 20: Addressing ScopeGlobal nonambiguityGlobal address identifies unique systemThere is only one system with address XGlobal applicabilityIt is possible at any system (any address) to identify any other system (address) by the global address of the other systemAddress X identifies that system from anywhere on the networke.g. MAC address on IEEE 802 networks
اسلاید 21: Connection IdentifiersConnection oriented data transfer (virtual circuits)Allocate a connection name during the transfer phaseReduced overhead as connection identifiers are shorter than global addressesRouting may be fixed and identified by connection nameEntities may want multiple connections - multiplexingState information
اسلاید 22: Addressing ModeUsually an address refers to a single systemUnicast addressSent to one machine or personMay address all entities within a domainBroadcastSent to all machines or usersMay address a subset of the entities in a domainMulticastSent to some machines or a group of users
اسلاید 23: MultiplexingSupporting multiple connections on one machineMapping of multiple connections at one level to a single connection at anotherCarrying a number of connections on one fiber optic cableAggregating or bonding ISDN lines to gain bandwidth
اسلاید 24: Transmission ServicesPrioritye.g. control messagesQuality of serviceMinimum acceptable throughputMaximum acceptable delaySecurityAccess restrictions
اسلاید 25: OSI - The ModelA layer modelEach layer performs a subset of the required communication functionsEach layer relies on the next lower layer to perform more primitive functionsEach layer provides services to the next higher layerChanges in one layer should not require changes in other layers
اسلاید 26: The OSI Environment
اسلاید 27: OSI as Framework for Standardization
اسلاید 28: Layer Specific Standards
اسلاید 29: Elements of StandardizationProtocol specificationOperates between the same layer on two systemsMay involve different operating systemProtocol specification must be preciseFormat of data unitsSemantics of all fieldsallowable sequence of PCUsService definitionFunctional description of what is providedAddressingReferenced by SAPs
اسلاید 30: OSI Layers (1)PhysicalPhysical interface between devicesMechanicalElectricalFunctionalProceduralData LinkMeans of activating, maintaining and deactivating a reliable linkError detection and controlHigher layers may assume error free transmission
اسلاید 31: OSI Layers (2)NetworkTransport of informationHigher layers do not need to know about underlying technologyNot needed on direct linksTransportExchange of data between end systemsError freeIn sequenceNo lossesNo duplicatesQuality of service
اسلاید 32: OSI Layers (3)SessionControl of dialogues between applicationsDialogue disciplineGroupingRecoveryPresentationData formats and codingData compressionEncryptionApplicationMeans for applications to access OSI environment
اسلاید 33: Use of a Relay
اسلاید 34: TCP/IP Protocol SuiteDominant commercial protocol architectureSpecified and extensively used before OSIDeveloped by research funded US Department of DefenseUsed by the Internet
اسلاید 35: TCP/IP Protocol Architecture(1)Application LayerCommunication between processes or applicationsEnd to end or transport layer (TCP/UDP/…)End to end transfer of dataMay include reliability mechanism (TCP)Hides detail of underlying networkInternet Layer (IP)Routing of data
اسلاید 36: TCP/IP Protocol Architecture(2)Network LayerLogical interface between end system and networkPhysical LayerTransmission mediumSignal rate and encoding
اسلاید 37: PDUs in TCP/IP
اسلاید 38: Some Protocols in TCP/IP Suite
اسلاید 39: Required ReadingStallings chapter 2Comer,D. Internetworking with TCP/IP volume IComer,D. and Stevens,D. Internetworking with TCP/IP volume II and volume III, Prentice HallHalsall, F> Data Communications, Computer Networks and Open Systems, Addison WesleyRFC
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