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Chapter 2 Reference Models

Chapter 2 Reference Models. Compiled By: Ashish Kr. Jha. Chapter 2:Reference Models 2.1 Protocols and Standards 2.2 Interfaces and Services 2.3 OSI Layers 2.4 TCP/IP Layers 2.5 Comparison of OSI & TCP/IP 2.6 Networking hardware: NIC, Hub, Repeater, Switches, Bridge, Router.

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Chapter 2 Reference Models

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  1. Chapter 2Reference Models Compiled By: Ashish Kr. Jha

  2. Chapter 2:Reference Models 2.1 Protocols and Standards 2.2 Interfaces and Services 2.3 OSI Layers 2.4 TCP/IP Layers 2.5 Comparison of OSI & TCP/IP 2.6 Networking hardware: NIC, Hub, Repeater, Switches, Bridge, Router Compiled By: Ashish Kr. Jha

  3. Protocols andStandards • NetworkProtocols • Protocol suites are collections of protocols that enablenetwork communication betweenhosts. • A protocol is a formal description of a set of rules and conventions that govern a particular aspect of how devices on a network communicate. Protocols determine the format, timing, sequencing, and error control in datacommunication. • Without protocols, the computer cannot make or rebuild the stream of incoming bits from another computer into the originalformat. Compiled By: Ashish Kr. Jha

  4. Protocols andStandards • Protocols control all aspects of data communication, which include thefollowing: • ▫ How the physical network isbuilt • ▫ How computers connect to thenetwork • ▫ How the data is formatted fortransmission • ▫ How that data issent • ▫ How to deal witherrors • These network rules are created and maintained by many different organizations and committees. Included in these groups are the Institute of Electrical and Electronic Engineers (IEEE),American National Standards Institute (ANSI), Telecommunications Industry Association (TIA), Electronic Industries Alliance (EIA) and the International Telecommunications Union(ITU). Compiled By: Ashish Kr. Jha

  5. LayeredArchitecture • Layer architecture simplifies the networkdesign. • It is easytodebugnetworkapplicationsinalayeredarchitecturenetwork. • The networkmanagementiseasierduetothelayered architecture. • Network layers follow a set of rules, calledprotocol. • The protocol defines the format of the data being exchanged, and the control and timing for the handshake betweenlayers. Compiled By: Ashish Kr. Jha

  6. ReferenceModel • There are basically two referencemodel: • ▫ OSI referencemodel • ▫ TCP/IP referencemodel Compiled By: Ashish Kr. Jha

  7. Open System Interconnection (OSI) ReferenceModel • The OSI reference model is a framework that is used to understand how information travels throughout anetwork. • The OSI reference model explains how packets travel through the various layers to another device on a network, even if the sender and destination have different types of networkmedia. Compiled By: Ashish Kr. Jha

  8. OSI ReferenceModel • In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function. Dividing the network into seven layers provides the following advantages: • ▫ It breaks network communication into smaller, more manageable parts. • ▫ It standardizes network components to allow multiple vendor development andsupport. • ▫ It allows different types of network hardware and software to communicate with eachother. • ▫ It prevents changes in one layer from affecting otherlayers. • ▫ It divides network communication into smaller parts to make • learning it easier tounderstand. Compiled By: Ashish Kr. Jha

  9. OSI Reference Model Compiled By: Ashish Kr. Jha

  10. Physical Layer (Layer1) • Concern with datatransmission • Wires and theirspecification • Connector for the system toconnect • Voltage (voltage at which the binary data is being assign and (transmitted) • Data rate ( rate at which bit istransmit) • Protocol Data Unit(PDU):bps Compiled By: Ashish Kr. Jha

  11. Data Link Layer (Layer2) • There is a direct link control on thenetwork • Provide reliable data transfer over thelink • Physicaladdressing • Networktopology • Error notification and flowcontrol • Protocol Data Unit(PDU):Frame Compiled By: Ashish Kr. Jha

  12. Network Layer (Layer3) • Networkaddress • Best path determination • Data transmission between thesubnet • Protocol Data Unit(PDU): Datagram /Packet Compiled By: Ashish Kr. Jha

  13. Transport Layer (Layer4) • End to endconnection • Process areaddressed • Transportation issue between thehost • Reliable data transfer between thehost • Establish connection between thehost • Flow control and congestioncontrol • Error detection andrecovery • Protocol Data Unit (PDU):Segment Compiled By: Ashish Kr. Jha

  14. Session Layer (Layer5) • Maintain the session of theuser • Tokenmanagement • Track all the event through theuse • Establish and terminatesession • Protocol Data Unit (PDU):Data Compiled By: Ashish Kr. Jha

  15. Presentation Layer (Layer6) • Datarepresentation • Ensure the data is read able by theapplication • Format ofdata • Data structureselection • Data transfer syntax andsemantics • eg. ASCII, UNICODEetc • Protocol Data Unit (PDU):Data Compiled By: Ashish Kr. Jha

  16. Application Layer (Layer7) • Application for the user for networkuse • Provide the different network services to theuser • Email, www, ftp, http, smtpetc. • Protocol Data Unit (PDU):Data Compiled By: Ashish Kr. Jha

  17. Design Issues ofLayers • Addressing • ErrorControl • FlowControl • Multiplexing/demultiplexing • Routing Compiled By: Ashish Kr. Jha

  18. Relationship of Services toProtocols • A service is a set of primitives (operations) that a layer provides to the layer aboveit. • The service defines what operations the layer is prepared to perform on behalf of its users, but it says nothing at all about how these operations areimplemented. • A service relates to an interface between two layers, with the lower layer being the service provider and the upper layer being the serviceuser. • A protocol, in contrast, is a set of rules governing the format and meaning of the packets, or messages that are exchanged by the peer entities within alayer. • Entities use protocols to implement their servicedefinitions. Compiled By: Ashish Kr. Jha

  19. Relationship of Services toProtocols Compiled By: Ashish Kr. Jha

  20. Header and TrailerAddition Compiled By: Ashish Kr. Jha

  21. TCP/IPModel • The U.S. Department of Defense (DoD) created the TCP/IP reference model, because it wanted to design a network that could survive any conditions, including a nuclearwar. • In a world connected by different types of communication media such as copper wires, microwaves, optical fibers and satellite links, the DoD wanted transmission of packets every time and under anyconditions. • Thisverydifficult design problem brought aboutthecreation oftheTCP/IPmodel. • TCP/IP was developed as an open standard. This meant that anyone was free to use TCP/IP. This helped speed up the development of TCP/IP as astandard. • The TCP/IP model has the following fourlayers: • ▫ Applicationlayer • ▫ Transport layer • ▫ Internet layer • ▫ Network access layer /Host-to-networklayer Compiled By: Ashish Kr. Jha

  22. TCP/IPModel Compiled By: Ashish Kr. Jha

  23. TCP/IPModel • Network AccessLayer • The lowest layer of the TCP/IP protocolhierarchy. • It defines how to use the network to transmit an IP datagram. Unlike higher-level protocols, Network Access Layer protocols must know the details of the underlying network (its packet structure, addressing, etc.) to correctly format the data being transmitted to comply with the networkconstraints. • The TCP/IP Network Access Layer can encompass the functions of all three lower layers of the OSI reference Model (Physical, Data Link and Networklayers). • As new hardware technologies appear, new Network Access protocols must be developed so that TCP/IP networks can use the new hardware. Consequently, there are many access protocols - one for each physical networkstandard. Compiled By: Ashish Kr. Jha

  24. TCP/IPModel • Internetlayer • Provides services that are roughly equivalent to the OSI Networklayer. • The primary concern of the protocol at this layer is to manage the connections across networks as information is passed from source to destination. • The Internet Protocol (IP) is the primary protocol at this layer of the TCP/IP model. • Transportlayer • It is designed to allow peer entities on the source and destinationhoststo carry on a conversation, just as in the OSI transportlayer. • Two end-to-end transport protocols have been defined here: TCP and UDP Compiled By: Ashish Kr. Jha

  25. TCP/IPModel • ApplicationLayer • Includes the OSI Session, Presentation and Applicationlayers. • An application is any process that occurs above the Transport Layer. This includes all of the processes that involve user interaction. The application determines the presentation of the data and controls the session. • There are numerous application layer protocols in TCP/IP, including Simple Mail Transfer Protocol (SMTP) and Post Office Protocol (POP) used for e-mail, Hyper Text Transfer Protocol (HTTP) used for the World-Wide-Web, and File Transfer Protocol(FTP). • Most application layer protocols are associated with one or more port number. Compiled By: Ashish Kr. Jha

  26. Typical Implementation ofLayers User Level Operating SystemLevel Hardware Level Compiled By: Ashish Kr. Jha

  27. ExampleNetworks • TheInternet • X.25 • FrameRelay • Ethernet • VOIP • NGN • MPLS • xDSL Compiled By: Ashish Kr. Jha

  28. Comparison between OSI and TCP/IP Compiled By: Ashish Kr. Jha

  29. OSI & TCP/IP Similarities • The OSI & TCP/IP have much in common • Both based on the concept of stack of independent protocols. • The functionality of the layers is roughly similar. • For e.g. in both models the layers up through & including the transport layer are there to provide end to end network independent transport service to processes wishing to communicate. • These layers form the transport provider. • Again in both the models, layer above transport are application oriented users of the transport service. Compiled By: Ashish Kr. Jha

  30. OSI & TCP/IP Differences • OSI model clearly defined the distinction between services, interfaces and protocols, where the TCP/IP model does not. • Each layer performs some services for the layers above it • The service definition says what the layer does, not how entities above it access it & how the layer works. • It defines the layer’s semantics . • A layer’s interface tells the processes above it how to access it. • It specifies what parameters are & what results to expect. • It too says nothing about how layers work inside. • Finally, the peer protocols used in a layer are the layer’s own business. Compiled By: Ashish Kr. Jha

  31. The Differences (cont’d) • It can use any protocols it wants to, as long as it gets the job done. • It can also change them at will without affecting software in higher layers. • This fits in nicely with OO programming concepts as the layer hide information. • An object, like a layer, has a set of methods(operations) that processes outside the object can invoke. • The semantics of these methods define the set of services that the object offers. • The methods’ parameters & results from the object’s interface. • The code internal to the object is its protocol and not visible outside the object. • As a consequence, the protocol in OSI layers are better hidden than in the TCP/IP model and can easily be replaced as the technology changes but difficult in the TCP/IP model. Compiled By: Ashish Kr. Jha Compiled By: Ashish Kr. Jha

  32. The Differences (cont’d) • The OSI model has no biases for protocols, but the OSI model was overly general and did not help with the creation of new protocols. • OSI supports connectionless and connection-oriented in the network layer, but only connection-oriented in the transport layer, providing no choice to the user. • TCP/IP supports only connectionless in the network layer, but both in the transport layer, giving user a choice. Compiled By: Ashish Kr. Jha Compiled By: Ashish Kr. Jha

  33. Networking Devices HUB, Switches, Routers, ,Modems etc. Compiled By: Ashish Kr. Jha

  34. NetworkingDevices • ACollisionDomainisasectionofnetworkwherepacketcollisions canoccuriftwonodes attempttocommunicateatthesametime. • A BroadcastDomainincludesallofthehoststhatabroadcast frametransmittedbyasingle host canreach. • Repeater: • Physical LayerDevice. • Regeneratesthesignal. • Extendthedistanceoverwhichasignal may • traveldowna cable. 200m • Collisiondomain=1 • Broadcastdomain=1 100m 100m Repeater Compiled By: Ashish Kr. Jha

  35. NetworkingDevices Hub: • MultiportRepeater • A central point of a star topology and allows the multiple connectionsof devices. • InrealityaHubisaRepeaterwithmultipleportsFunctionsin a similarmannertoaRepeater. • Hub works at the Physical Layer of the OSI model. Passes • datano matter whichdeviceitis addressedto. • Collisiondomain= 1 • • • • Broadcastdomain=1 TwoTypes HUB Active Hub • RegeneartesSignal,needspower • PassiveHub • AsimpleConnector(nosignalRegeneration) • Compiled By: Ashish Kr. Jha

  36. 5 • NetworkingDevices • Bridge: • DataLinkLayerDevice • MaintainsMACtablewithMACaddressandportno.and decideswhethertoforwardtheframeornot. • DividesNetworkintodifferentLANSegments • SmarterthanRepeaters • Collisiondomain=2(#LANSegments) • Broadcastdomain=1 Compiled By: Ashish Kr. Jha

  37. NetworkingDevices(Bridge) Compiled By: Ashish Kr. Jha

  38. NetworkingDevices • Switch: • MultiportBridge • A switchisessentiallyafast,multi-portbridgethatcancontain dozens ofports. • A switchdynamicallybuildsandmaintainsaMACtable,which • holds allofthenecessaryMAC informationforeachport. • Theswitch thenforwardsordiscardsframesbasedonthetable entries. • TableentriesarecalledContentAddressableMemory. • SwitchworksatDatalinkLayerofOSIReferencemodel Compiled By: Ashish Kr. Jha

  39. NetworkingDevices • Switch • DataLinkLayerDevice • AMultiport Bridge • DividesNetworkinto differentLANSegments • Collisiondomain=no. ofports • Broadcastdomain=1 Switch DataLinkLayer Physical Layer Physical Layer Compiled By: Ashish Kr. Jha

  40. NetworkingDevices (a)Ahub. (b)Abridge. (c)aswitch. Compiled By: Ashish Kr. Jha

  41. NetworkingDevices • Router: • Arouterisaspecialtypeofcomputer. It has thesamebasic componentsasastandarddesktopPC. IthasaCPU,memory,asystembus,andvariousinput/output interfaces. • • • However,routersaredesignedtoperformsomeveryspecific functionsthatarenot typicallyperformedbydesktopcomputers. • Forexample,routersconnectandallowcommunicationbetween twonetworksanddeterminethebestpathfordatatotravelthrough theconnectednetworks. • RouterworksatNetworkLayerofOSIReferencemodel. Compiled By: Ashish Kr. Jha

  42. NetworkingDevices • Routers: • NetworkLayerDevice. • AbletoanalyseNetworklayer addressandfindtheroute. • MaintainsRoutingtabletoroutepackettodestinationaddress. • Expensive andSlowerthanswitch. • SupportsHierarchicaladdressing. • “UseSwitchwhere you can, UseRouterwhereyoumust.” NetworkLayer DataLinkLayer PhysicalLayer Compiled By: Ashish Kr. Jha

  43. NetworkDevices • NetworkInterfaceCard(NIC): • ANICisaprintedcircuitboardthatfitsintotheexpansionslotofa busonacomputermotherboard. • It canalsobeaperipheraldevice. • NICs aresometimescallednetworkadapters. • Each NIC is identified byauniquecodecalledaMediaAccess used tocontroldata • Control(MAC)address.Thisaddressis communicationforthehost onthenetwork. • Asthenameimplies,theNIC • controlshostaccesstothenetwork. • NIC worksatDatalinklayerofOSI Referencemodel. Compiled By: Ashish Kr. Jha

  44. NetworkingDevices • Gateway: • Gatewayisaserverthatappearstotheclientasifitwereanorigin server. • Allowsdifferentnetworkstocommunicatebyofferingatranslation • servicefromone protocolstacktoanother. • Gatewayactsonbehalfoftheotherserversthatmaynotableto communicatedirectlywithclients. • Allows devicesindifferentnetworkstocommunicate • Generictermforrouters • Theterm“gateway”isalsousedfordevicethatinterconnects differentNetworksandwhichperformtranslationof protocols(Multi-ProtocolRouters). Network1 Network2 Gateway Compiled By: Ashish Kr. Jha

  45. What is the difference between? • Bridge: device to interconnect two LANs • Router: device to interconnect SIMILAR networks, e.g. similar protocols and workstations and servers • Gateway: device to interconnect DISSIMILAR protocols and servers, and Macintosh and IBM LANs and equipment Compiled By: Ashish Kr. Jha

  46. Assignment: • Explain in brief OSI reference model. • Explain the function of TCP/IP layer briefly. • Define interfaces and services. How does a switch differ from a hub? Explain. • Explain in brief the types of services provided by network layer to its upper layer. • Write about hub and repeater. • Compare and contrast between OSI and TCP/IP. • What are three reasons for having layered protocol? Also mention two advantages and dis disadvantages of having international standard for network protocols.

  47. Compiled By: Ashish Kr. Jha

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