Computer Networks with Internet TechnologyWilliam StallingsChapter 2Protocols and the TCP/IP Protocol Suite

Need For Protocol ArchitectureE.g. File transferSource must activate communication path or inform network of destinationSource must check destination is prepared to receiveFile transfer application on source must check destination file management system will accept and store file for his userMay need file format translationTask broken into subtasksImplemented separately in layers in stackFunctions needed in both systemsPeer layers communicate

Key Elements of a ProtocolThe peer layers communicates by means of formatted blocks of data that obey a set of rules and conventions known as a protocol.Key elements:SyntaxFormat of the data blocksSignal levelsSemanticsControl information for coordination and error handlingTimingSpeed matchingSequencing

2.2 Protocol ArchitectureTask of communication broken up into modulesFor example, file transfer could use three modules:File transfer applicationCommunication service moduleNetwork access module

Figure 2.1 Simplified Architecture for File Transfer

Figure 2.2 Protocol Architectures and Networks

Addressing RequirementsTwo levels of addressing requiredEach computer needs unique network addressEach application on a (multi-tasking) computer needs a unique address within the computerThe service access point or SAPThe port on TCP/IP stacks

Figure 2.3 Protocols in Simplified Architecture

Protocol Data Units (PDU)At each layer, protocols are used to communicateControl information is added to user data at each layer (PDU = Control + Data)Transport layer may fragment user dataEach fragment has a transport header addedDestination SAP (port)Sequence numberError detection codeThis gives a transport protocol data unit

Figure 2.4 Protocol Data Units

Figure 2.5 Operation of a Protocol Architecture

Standardized Protocol ArchitecturesRequired for devices to communicateVendors have more marketable productsCustomers can insist on standards based equipmentTwo standards:OSI Reference modelNever lived up to early promisesTCP/IP protocol suiteMost widely used

2.3 OSIOpen Systems InterconnectionDeveloped by the International Organization for Standardization (ISO)Seven layersA theoretical system delivered too late!TCP/IP is the de facto standard

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

Figure 2.6OSI Layers

Figure 2.7The OSI Environment

Figure 2.8 OSI as Framework for Standardization

Figure 2.9Layer Specific Standards

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 PDUsService definitionFunctional description of what is providedAddressingReferenced by SAPs

Service Primitives and ParametersServices between adjacent layers expressed in terms of primitives and parametersPrimitives specify function to be performedParameters pass data and control info

Primitive Types

REQUEST A primitive issued by a service user to invoke some service and to pass the parameters needed to specify fully the requested service INDICATION A primitive issued by a service provider either to: indicate that a procedure has been invoked by the peer service user on the connection and to provide the associated parameters, or notify the service user of a provider-initiated action RESPONSE A primitive issued by a service user to acknowledge or complete some procedure previously invoked by an indication to that user CONFIRM A primitive issued by a service provider to acknowledge or complete some procedure previously invoked by a request by the service user

Service Primitive TypesRequestIndicationResponseConfirm

Figure 2.10 Timing Sequence for Service Primitives

2.4 TCP/IP Protocol ArchitectureDeveloped by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)Used by the global InternetNo official model but a working one. Application layer Transport layer Internet layerNetwork access layer Physical layer(host-to-host)(Data Link Layer)

Physical LayerPhysical interface between data transmission device (e.g. computer) and transmission medium or networkCharacteristics of transmission mediumSignal levelsData ratesetc.

Network Access LayerExchange of data between end system and networkDestination address provisionInvoking services like priority

Internet Layer (IP)Systems may be attached to different networksRouting functions across multiple networksImplemented in end systems and routers

Copyright 2015 Pearson Education, Ltd. 1-*Physical and Data links

Copyright 2015 Pearson Education, Ltd.

Copyright 2015 Pearson Education, Ltd. 1-*Hybrid Switched/Wireless Network

Copyright 2015 Pearson Education, Ltd.

Transport Layer (TCP)Reliable delivery of dataOrdering of deliveryApplication LayerSupport for user applicationse.g. http, SMTP

Transport and Application ProcessesCopyright 2015 Pearson Education, Ltd.

Copyright 2015 Pearson Education, Ltd.

Figure 2.11OSI v TCP/IPInternetStandardsIEEEISOITU-T

Some Protocols in TCP/IP Suite

TCPUsual transport layer is Transmission Control ProtocolReliable connectionConnectionTemporary logical association between entities in different systemsTCP PDU Called TCP segmentIncludes source and destination port (c.f. SAP)Identify respective users (applications)Connection refers to pair of portsTCP tracks segments between entities on each connection

UDPAlternative to TCP is User Datagram ProtocolNot guaranteed deliveryNo preservation of sequenceNo protection against duplicationMinimum overheadAdds port addressing to IP

TCP and UDP Headers

IP and IPv6IP (v4) headerminimum 20 octets (160 bits)32-bit source and destination addressesChecksum applies to header to avoid incorrect deliveryProtocol field shows if TCP, UDP etc. carriedFlags and fragmentation offset used in fragmentationIPv61995 IPng became standard IPv6 in 1996Enhancements for modern high speed networksCarry multimedia data streamsIncrease address space (128 bits)

Figure 2.13 (a)IPv4 Header

Figure 2.13 (b)IPv6 Header

Figure 2.14TCP/IP Concepts

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)

Trace of Simple OperationProcess associated with port 1 in host A sends message to port 2 in host BProcess at A hands down message to TCP to send to port 2TCP hands down to IP to send to host BIP hands down to network layer (e.g. Ethernet) to send to router JGenerates a set of encapsulated PDUs

Figure 2.15PDUs in TCP/IP

TCP Header + Telnet DataTelnet Data

IP Header + TCP Header + Telnet DataEthernet Frame Header + IP Header + TCP Header + Telnet Data

Example Header InformationDestination portSequence numberChecksum

InternetworkingMost networks not isolatedDifferent types of LANMultiple similar LANsMultiple sites connected by WAN(s) May appear as large networkEntire configuration referred to as an internetEach constituent network is a subnetwork

Internetworking DevicesEach subnetwork supports communication among devices attached to that subnetworkEnd systems (ESs)Subnetworks connected by intermediate systems (ISs)Provide communications path and relay and routing functionsBridges and routersDifferent types of protocols usedBridge operates at layer 2Relay between like networksRouter operates at layer 3Routes packets between potentially different networks

RoutersInterconnect dissimilar subnetworksProvide a link between networksProvide for routing and delivery of data between processes on end systems attached to different networksDo not require modifications of architecture of subnetworksMust accommodate differences among networksAddressing schemesMaximum packet sizesInterfacesReliabilitySatisfied by internetworking protocol implemented in all end systems and routersIP

Figure 2.16 Configuration for TCP/IP ExampleATM: Asynchronous Transfer Mode

Action of Sender

Action of Router

Figure 2.19Action ofReceiver

Internetworking Terminology (1)InternetCollection of communication networks interconnected by bridges and/or routersIntranetAn internet used by single organizationProvides key Internet applications (World Wide Web)Operates within organization for internal purposesCan exist as isolated, self-contained internetMay have links to the InternetSubnetworkRefers to a constituent network of an internet. This avoids ambiguity because the entire internet, from a user's point of view, is a single network

Internetworking Terminology (2)End System (ES)Device attached to one of the networks of an internetSupports end-user applications or servicesIntermediate System (IS)Device used to connect two networksPermits communication between ES attached to different networksBridgeIS used to connect two LANs that use similar protocolsAddress filterDoes not modify packetsLayer 2 of the OSI modelRouterIS used to connect two networks that may or may not be similarUses an internet protocol present in each router and each end system of the networkLayer 3 of the OSI model"Switch" can be regarded as a multiport bridge.

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