OSI

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OSI (open System Interconnection) Developed By ISO (International Organization for Standardization )

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OSI

  1. 1. The Layered Model© 1999, Cisco Systems, Inc. www.cisco.com
  2. 2. Layered CommunicationLocation A Ik hou Message van konijnen L: EN Information for the I like Remote rabbits Translator Fax #:--- Information L: EN for the I like Remote rabbits Secretary Source: Tanenbaum, 1996
  3. 3. Layered CommunicationLocation A Location B Ik hou J’aime Message van les lapins konijnen L: EN Information L: EN for the I like I like Remote rabbits Translator rabbits Fax #:--- Fax #:--- Information L: EN L: EN for the I like I like Remote rabbits Secretary rabbits
  4. 4. Layered CommunicationLocation A Location B Layers Ik hou J’aime van Message 3 les lapins konijnen L: EN Information L: EN I like for the remote 2 I like rabbits rabbits translator Fax #:--- Fax #:--- Information L: EN L: EN for the I like I like remote rabbits secretary 1 rabbits
  5. 5. Why a Layered Network Model?7 Application • Reduces complexity (one big problem to seven smaller ones)6 Presentation • Standardizes interfaces5 Session • Facilitates modular engineering4 Transport • Assures interoperable technology3 Network • Accelerates evolution2 Data Link • Simplifies teaching and learning1 Physical
  6. 6. Devices Function at Layers 7 Application 6 PresentationNIC Card 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Hub
  7. 7. Host Layers }7 Application6 Presentation Host layers: Provide accurate5 Session data delivery between computers4 Transport3 Network2 Data Link1 Physical
  8. 8. Media Layers }7 Application6 Presentation Host layers: Provide accurate5 Session data delivery between computers4 Transport }3 Network2 Data Link Media layers: Control1 Physical physical delivery of messages over the network
  9. 9. Layer Functions7 Application Provides network services to application processes (such as electronic mail, file transfer, and terminal emulation)
  10. 10. Layer Functions7 Application Network 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. 11. Layer Functions7 Application Network services to applications6 Presentation Data representation5 Session Inter-host communication • Establishes, manages, and terminates sessions between applications
  12. 12. Layer Functions7 Application Network services to applications6 Presentation Data representation5 Session Inter-host communication4 Transport 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. 13. Layer Functions7 Application Network services to applications6 Presentation Data representation5 Session Inter-host communication4 Transport End-to-end connection reliability3 Network Addresses and best path • Provides connectivity and path selection between two end systems • Domain of routing
  14. 14. Layer Functions7 Application Network services to applications6 Presentation Data representation5 Session Inter-host communication4 Transport End-to-end connection reliability3 Network Addresses and best path2 Data Link Access to media • Provides reliable transfer of data across media • Physical addressing, network topology, error notification, flow control
  15. 15. Layer Functions7 Application Network services to applications6 Presentation Data representation5 Session Inter-host communication4 Transport End-to-end connection reliability3 Network Addresses and best path2 Data Link Access to media1 Physical Binary transmission • Wires, connectors, voltages, data rates
  16. 16. Peer-to-Peer Communications Host A Host B7 Application Application6 Presentation Presentation5 Session Session4 Transport Segments Transport3 Network Packets Network2 Data Link Frames Data Link1 Physical Bits Physical
  17. 17. Data Encapsulation Host A Host BApplication ApplicationPresentationSessionTransport } { Data Presentation Session TransportNetwork NetworkData Link Data LinkPhysical Physical
  18. 18. Data Encapsulation Host A Host BApplication ApplicationPresentationSessionTransport } { Data Network Data Header Presentation Session TransportNetwork NetworkData Link Data LinkPhysical Physical
  19. 19. Data Encapsulation Host A Host BApplication ApplicationPresentationSessionTransport } { Data Network Data Header Presentation Session TransportNetwork Network Frame Network Data FrameData Link Data Link Header Header TrailerPhysical Physical
  20. 20. Data Encapsulation Host A Host BApplication ApplicationPresentationSessionTransport } { Data Network Data Header Presentation Session TransportNetwork Network Frame Network Data FrameData Link Data Link Header Header TrailerPhysical Physical 0101101010110001
  21. 21. Layers 1 & 2: Physical & Data Link Layers© 1999, Cisco Systems, Inc. www.cisco.com
  22. 22. Physical and Logical Addressing0000.0c12.3456
  23. 23. MAC Address 24 bits 24 bits Vendor Code Serial Number 0000.0c12. 3456 ROM RAM• MAC address is burned into ROM on a network interface card
  24. 24. Layer 3: Network Layer© 1999, Cisco Systems, Inc. www.cisco.com
  25. 25. Network Layer: Path Determination Which Path? Which Path?• Layer 3 functions to find the best path through the internetwork
  26. 26. Network Layer: Communicate Path 5 2 9 6 8 4 10 11 1 3 7 Addresses represent the path of media connections Routing helps contain broadcasts
  27. 27. Addressing—Network and Node Network Node 1 1 2.1 2 3 1.2 2 1 1.3 1.1 3.1 3 1• Network address—Path part used by the router• Node address—Specific port or device on the network
  28. 28. Protocol Addressing VariationsGeneral Network NodeExample 1 1 Network Host TCP/IPExample 10. 8.2.48 (Mask 255.0.0.0) Network NodeNovell IPX Example 1aceb0b. 0000.0c00.6e25
  29. 29. Network Layer Protocol OperationsX Y C C A A Each router provides its services to support upper layer functions
  30. 30. Network Layer Protocol Operations X Y C C A A B B Host X Host Y Application Application Presentation Presentation Session Router A Router B Router C Session Transport Transport Network Network Network Network Network Data Link Data Link Data Link Data Link Data Link Physical Physical Physical Physical Physical Each router provides its services to support upper layer functions
  31. 31. Routed Versus Routing Protocol• Routed protocol used between routers to direct user traffic Examples: IP, IPX, AppleTalk, DECnet Network Destination Exit Port Protocol Network to Use Protocol Name 1.0 1.1 2.0 2.1 3.0 3.1
  32. 32. Routed Versus Routing Protocol• Routed protocol used between routers to direct user traffic Examples: IP, IPX, AppleTalk, DECnet• Routing protocol used only between routers to maintain routing tables Examples: RIP, IGRP, OSPF
  33. 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. 34. Static Route Example Point-to-point or A A circuit-switched connection Only a single network connection with no need B B for routing updates ―Stub‖ network Fixed route to address reflects administrator’s knowledge
  35. 35. Adapting to Topology Change A A B B D D C C Can an alternate route substitute for a failed route?
  36. 36. Adapting to Topology Change A A B B X D D C C
  37. 37. Adapting to Topology Change A A B B X D D C C Can an alternate route substitute for a failed route? Yes—With dynamic routing enabled
  38. 38. Layers 4–7: Transport, Session, Presentation, and Application Layers© 1999, Cisco Systems, Inc. www.cisco.com
  39. 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. 40. Transport Layer— Segments Upper-Layer ApplicationsApplication Electronic File TerminalPresentation Mail Transfer SessionSessionTransport Application Application Data Data Port Port Segments
  41. 41. Transport Layer—Establishes ConnectionSender Receiver Synchronize Negotiate Connection Synchronize Acknowledge Connection Established Data Transfer (Send Segments)
  42. 42. Transport Layer—Sends Segments with Flow Control TransmitSender Receiver Buffer Full Not Ready Stop Process Segments Go Ready Buffer OK Resume Transmission
  43. 43. Transport Layer— Reliability with Windowing • Window Size = 1 Send 1 Receive 1 Ack 2Sender Send 2 Receive 2 Receiver Ack 3 • Window Size = 3 Send 1 Receive 1 Send 2 Receive 2 Sender Send 3 Receive 3 Receiver Ack 4 Send 4
  44. 44. Transport Layer— An Acknowledgement Technique Sender Receiver1 2 3 4 5 6 7 1 2 3 4 5 6 7 Send 1 Send 2 Send 3 Ack 4 Send 4 Send 5 Send 6 Ack 5 Send 5 Ack 7
  45. 45. Transport to Network Layer End-to-End Segments Routed Packets
  46. 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 as they interact on different hosts
  47. 47. Presentation Layer • Text • Graphics • Data • Visual images ASCII PICT login: EBCDIC TIFF Encrypted JPEG • Sound GIF MIDI • Video MPEG QuickTime Provides code formatting and conversion for applications
  48. 48. Application Layer COMPUTER APPLICATIONS NETWORK Word Processor APPLICATIONS INTERNETWORK Presentation Graphics Electronic Mail APPLICATIONS Spreadsheet File Transfer Electronic Data Interchange Database Remote Access World Wide Web Design/Manufacturing Client-Server Process E-Mail Gateways Project Planning Information Location Special-Interest Bulletin Boards Others Network Management Financial Transaction Services Others Internet Navigation Utilities Conferencing (Voice,Video, Data) Others Internetwork applications can extend beyond the enterprise (i.e., to suppliers, etc.)
  49. 49. Summary OSI reference model describes building blocks of functions for program-to-program communications between similar or dissimilar hosts Layers 4–7 (host layers) provide accurate data delivery between computers Layers 1–3 (media layers) control physical delivery of data over the network

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