1. The Layered Model 1999, Cisco Systems, Inc. www.cisco.com

2. Layered CommunicationLocation A Ik houMessage van konijnenL: EN Informationfor theI likeRemoterabbits TranslatorFax #:--- InformationL: EN for theI likeRemoterabbits SecretarySource: Tanenbaum, 1996 3. Layered CommunicationLocation ALocation B Ik houJaimeMessage van les lapins konijnenL: EN InformationL: ENfor theI likeI likeRemoterabbits Translator rabbits Fax #:---Fax #:--- InformationL: ENL: EN for theI like I likeRemoterabbits Secretaryrabbits 4. Layered CommunicationLocation A Location BLayers Ik hou Jaime vanMessage3 les lapins konijnenL: EN Information L: ENI likefor theremote2 I likerabbitsrabbits translatorFax #:---Fax #:--- Information L: ENL: EN for theI likeI likeremoterabbits secretary 1 rabbits 5. Why a Layered Network Model?7Application Reduces complexity (one bigproblem to seven smaller ones)6Presentation Standardizes interfaces5Session Facilitates modular engineering4Transport Assures interoperable technology3Network Accelerates evolution2Data Link Simplifies teaching and learning1Physical 6. Devices Function at Layers 7 Application 6 PresentationNIC Card 5 Session 4 Transport 3 Network 2 Data Link 1 PhysicalHub 7. Host Layers }7 Application6 Presentation Host layers: Provide accurate5 Sessiondata delivery between computers4 Transport3 Network2 Data Link1 Physical 8. Media Layers}7Application6PresentationHost layers: Provide accurate5Session data delivery between computers4Transport}3Network2Data LinkMedia layers: Control1Physical physical delivery of messages overthe network 9. Layer Functions7 Application Provides network services to applicationprocesses (such as electronic mail, file transfer,and terminal emulation) 10. Layer Functions7 ApplicationNetwork services to applications6 Presentation Data representation Ensures data is readable by receiving system Format of data Data structures Negotiates data transfer syntax for application layer 11. Layer Functions7 ApplicationNetwork services to applications6 Presentation Data representation5 SessionInter-host communication Establishes, manages, and terminates sessions between applications 12. Layer Functions7 ApplicationNetwork services to applications6 Presentation Data representation5 SessionInter-host communication4Transport End-to-end connection reliability Concerned with data transport issues between hosts Data transport reliability Establishes, maintains, and terminates virtual circuits Fault detection and recovery Information flow control 13. Layer Functions7 ApplicationNetwork services to applications6 Presentation Data representation5 SessionInter-host communication4Transport End-to-end connection reliability3 NetworkAddresses and best path Provides connectivity and path selection between two end systems Domain of routing 14. Layer Functions7 ApplicationNetwork services to applications6 Presentation Data representation5 SessionInter-host communication4Transport End-to-end connection reliability3 NetworkAddresses and best path2 Data LinkAccess to media Provides reliable transfer of data across media Physical addressing, network topology, error notification, flow control 15. Layer Functions7ApplicationNetwork services to applications6Presentation Data representation5SessionInter-host communication4 Transport End-to-end connection reliability3NetworkAddresses and best path2Data Link Access to media1PhysicalBinary transmission Wires, connectors, voltages, data rates 16. Peer-to-Peer CommunicationsHost AHost B7 Application Application6 PresentationPresentation5 Session Session4 TransportSegments Transport3 NetworkPacketsNetwork2 Data LinkFrames Data Link1 Physical Bits Physical 17. Data Encapsulation Host AHost BApplicationApplicationPresentationSessionTransport } { DataPresentation Session TransportNetworkNetworkData LinkData LinkPhysical Physical 18. Data Encapsulation Host AHost BApplicationApplicationPresentationSessionTransport } {DataNetwork DataHeader Presentation Session TransportNetworkNetworkData LinkData LinkPhysical Physical 19. Data Encapsulation Host AHost BApplicationApplicationPresentationSessionTransport } {Data Network Data Header Presentation Session TransportNetworkNetwork FrameNetwork Data FrameData LinkData Link Header Header TrailerPhysical Physical 20. Data Encapsulation Host AHost BApplicationApplicationPresentationSessionTransport } {Data Network Data Header Presentation Session TransportNetworkNetwork FrameNetwork Data FrameData LinkData Link Header Header TrailerPhysical Physical0101101010110001 21. Layers 1 & 2: Physical & Data Link Layers 1999, Cisco Systems, Inc. www.cisco.com 22. Physical and Logical Addressing0000.0c12.3456 23. MAC Address24 bits24 bits Vendor Code Serial Number 0000.0c12. 3456ROMRAM MAC address is burned into ROM on a networkinterface card 24. Layer 3: Network Layer 1999, Cisco Systems, Inc. www.cisco.com 25. Network Layer: Path Determination Which Path? Which Path? Layer 3 functions to find the bestpath through the internetwork 26. Network Layer: Communicate Path52 96 8410 111 37 Addresses represent the path of mediaconnections Routing helps contain broadcasts 27. AddressingNetwork and NodeNetwork Node 112.1231.2 21 1.3 1.1 3.1 31 Network addressPath part used by the router Node addressSpecific port or device on the network 28. Protocol Addressing VariationsGeneralNetworkNodeExample1 1 NetworkHost TCP/IPExample 10.8.2.48(Mask 255.0.0.0) NetworkNodeNovell IPX Example 1aceb0b. 0000.0c00.6e25 29. Network Layer Protocol OperationsXYCCAA Each router provides its services to supportupper layer functions 30. Network Layer Protocol OperationsXY C C A A B B Host X Host YApplicationApplicationPresentation PresentationSessionRouter ARouter BRouter CSessionTransportTransportNetworkNetwork Network Network NetworkData LinkData Link Data Link Data Link Data LinkPhysical PhysicalPhysicalPhysicalPhysical Each router provides its services tosupport upper layer functions 31. Routed Versus Routing Protocol Routed protocolused betweenrouters to directuser traffic Examples: IP, IPX, AppleTalk, DECnetNetwork Destination Exit PortProtocol Network to UseProtocol Name1.01.1 2.02.1 3.03.1 32. Routed Versus Routing Protocol Routed protocolused betweenrouters to directuser traffic Examples: IP, IPX, AppleTalk, DECnet Routing protocolused only betweenrouters to maintainrouting tables Examples: RIP, IGRP, OSPF 33. Static Versus Dynamic RoutesStatic Route Uses a protocol route that a network administrator enters into the routerDynamic Route Uses a route that a network protocol adjusts automatically for topology or traffic changes 34. Static Route ExamplePoint-to-point orAA circuit-switched connection Only a single networkconnection with no needB B for routing updates Stub network Fixed route to address reflectsadministrators knowledge 35. Adapting to Topology Change A ABB D DCC Can an alternate route substitutefor a failed route? 36. Adapting to Topology Change A ABBX D DCC 37. Adapting to Topology ChangeAA BB XDD CC Can an alternate route substitutefor a failed route?YesWith dynamic routing enabled 38. Layers 47: Transport, Session, Presentation, and Application Layers 1999, Cisco Systems, Inc. www.cisco.com 39. Transport Layer Segments upper-layer applications Establishes an end-to-end connection Sends segments from one end host to another Optionally, ensures data reliability 40. Transport LayerSegments Upper-Layer ApplicationsApplication ElectronicFileTerminalPresentationMail TransferSessionSessionTransportApplicationApplication DataData Port PortSegments 41. Transport LayerEstablishes ConnectionSenderReceiver Synchronize Negotiate ConnectionSynchronize Acknowledge Connection Established Data Transfer(Send Segments) 42. Transport LayerSends Segments with Flow Control TransmitSenderReceiverBuffer FullNot Ready StopProcessSegmentsGoReadyBuffer OKResume Transmission 43. Transport Layer Reliability with Windowing Window Size = 1Send 1 Receive 1 Ack 2SenderSend 2 Receive 2 Receiver Ack 3 Window Size = 3Send 1 Receive 1Send 2 Receive 2 SenderSend 3 Receive 3 Receiver Ack 4Send 4 44. Transport LayerAn Acknowledgement TechniqueSender Receiver1 2 3 4 56 7 1 234 5 6 7Send 1Send 2Send 3 Ack 4Send 4Send 5Send 6 Ack 5Send 5 Ack 7 45. Transport to Network Layer End-to-End SegmentsRouted Packets 46. Session Layer Network File System (NFS) Structured Query Language (SQL) Remote-Procedure Call (RPC) X Window System AppleTalk Session Protocol (ASP) DEC Session Control Protocol (SCP)Service Request Service Reply Coordinates applications asthey interact on different hosts 47. Presentation Layer Text Graphics Data Visual imagesASCII PICT login:EBCDICTIFFEncrypted JPEG Sound GIF MIDI VideoMPEGQuickTime Provides code formatting andconversion for applications 48. Application Layer COMPUTERAPPLICATIONSNETWORKWord Processor APPLICATIONS INTERNETWORKPresentation Graphics Electronic MailAPPLICATIONSSpreadsheet File Transfer Electronic Data InterchangeDatabaseRemote Access World Wide WebDesign/ManufacturingClient-Server Process E-Mail GatewaysProject PlanningInformation LocationSpecial-Interest Bulletin BoardsOthersNetwork ManagementFinancial Transaction ServicesOthersInternet Navigation UtilitiesConferencing (Voice,Video, Data)Others Internetwork applicationscan extend beyond theenterprise (i.e., to suppliers, etc.) 49. Summary OSI reference model describes building blocksof functions for program-to-programcommunications between similar or dissimilarhosts Layers 47 (host layers) provide accurate datadelivery between computers Layers 13 (media layers) control physicaldelivery of data over the network