1. OSI Reference Model

2. What is Protocol ? A protocol is a set of rules that make communication on a network more efficient. Operational sequence to carry our a specific task. Example : DNC, DHCP, HTTP.

3. Overview During the past two decades there has been a tremendous increase in the numbers and sizes of networks. Many of the networks, however, were built using different implementations of hardware and software. As a result, many of the networks were incompatible and it became difficult for networks using different specifications to communicate with each other.

4. International Organization for Standards (ISO) To address this problem, the International Organization for Standardization (ISO) researched many network schemes. The ISO recognized that there was a need to create a network model that would help network builders implement networks that could communicate and work together (interoperability) and therefore, released the OSI reference model in 1984.

5. The Layered Model

6. Layered CommunicationLocation A I like Message rabbits L: Dutch Information Ik hou for the Remote van Translator konijnen Fax #:--- Information L: Dutch for the Ik hou Remote van Secretary konijnen Source: Tanenbaum, 1996

7. Layered CommunicationLocation A Location B I like Jaime Message rabbits les lapins L: Dutch Information L: Dutch Ik hou for the Ik hou Remote van van Translator konijnen konijnen Fax #:--- Fax #:--- Information L: Dutch L: Dutch for the Ik hou Ik hou Remote van Secretary van konijnen konijnen

8. Layered CommunicationLocation A Location B Layers I like Jaime rabbits Message 3 les lapins L: Dutch Information L: Dutch Ik hou van for the remote 2 Ik hou van translator konijnen konijnen Fax #:--- Fax #:--- Information L: Dutch L: Dutch for the Ik hou Ik hou remote van secretary 1 van konijnen konijnen

9. Why a Layered Network Model? 7 Application Reduces complexity (one big problem to seven smaller 6 Presentation ones) 5 Session Standardizes interfaces 4 Transport Facilitates modular engineering 3 Network Assures interoperable 2 Data Link technology Accelerates evolution 1 Physical Simplifies teaching and learning

10. Devices Function at Layers 7 Application 6 PresentationNIC Card 5 Session 4 Transport 3 Network 2 Data Link 1 Physical Hub

11. Host Layers }7 Application6 Presentation Host layers: Provide accurate data delivery between5 Session computers4 Transport3 Network2 Data Link1 Physical

12. Media Layers }7 Application6 Presentation Host layers: Provide5 Session accurate data delivery between computers4 Transport }3 Network2 Data Link Media layers: Control physical delivery of messages1 Physical over the network

13. OSI Layers }7 Application6 Presentation Software layers5 Session4 Transport Heart of OSI }3 Network2 Data Link Hardware layers1 Physical

14. Layer Functions7 Application Provides network services to application processes (such as electronic mail, file transfer, and terminal emulation) Closest to User & Data Integrity.

15. Layer Functions7 Application Network services to applications6 Presentation Data representation Ensures data is readable by receiving system Translates between multiple data formats using a common data format. Encryption & Decryption Compression & Decompress.

16. Layer Functions7 Application Network services to applications6 Presentation Data representation5 Session Inter-host communication Establishes, manages, and terminates sessions between applications. Synchronizes Dialogue.

17. 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 Flow control

18. 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

19. 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 Physical addressing, network topology, Deliver of Frames. Error Detection (No correction) FCS

20. 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 Electrical & Mechanical Procedures. Wires, Connectors, Voltage Level, Timing of Voltage, Maximum transmission distance

21. Peer-to-Peer Communications Host A Host B7 Application Application6 Presentation Presentation5 Session Session Segments4 Transport Transport Packets3 Network Network Frames2 Data Link Data Link Bits1 Physical Physical

22. Data Encapsulation Host A Host B } {Application ApplicationPresentation Data PresentationSession SessionTransport TransportNetwork NetworkData Link Data LinkPhysical Physical

23. Data Encapsulation Host A Host B } {Application ApplicationPresentation Data PresentationSession SessionTransport Transport Network DataNetwork Header NetworkData Link Data LinkPhysical Physical

24. Data Encapsulation Host A Host B } {Application ApplicationPresentation Data PresentationSession SessionTransport Transport Network DataNetwork Header Network Frame Network Data FrameData Link Data Link Header Header TrailerPhysical Physical

25. Data Encapsulation Host A Host B } {Application ApplicationPresentation Data PresentationSession SessionTransport Transport Network DataNetwork Header Network Frame Network Data FrameData Link Data Link Header Header TrailerPhysical 0101101010110001 Physical

26. Layers 1 & 2:Physical & Data Link Layers

27. Physical and Logical Addressing0000.0c12.3456

28. 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

29. NIC - Addresses Two Addresses are associated with NICPhysical Address Logical Address MAC IP (Media Access Control) (Internet Protocol) L2 Address L3 Address Permanent Logical (Can be Changed) 48 Bit 32 Bit Hexadecimal Notation Dotted Decimal Notation Ex : 01-5C-D9-6B-03-2E Ex : 192.168.6.1

30. Layer 3:Network Layer

31. Network Layer: Path Determination Which Path? Which Path? Layer 3 functions to find the best path through the internetwork

32. Network Layer Protocol OperationsX Y C C A A Each router provides its services to support upper layer functions

33. Network Layer Protocol Operations X Y C C A A B B Host X Host YApplication ApplicationPresentation PresentationSession Router A Router B Router C SessionTransport TransportNetwork Network Network Network NetworkData Link Data Link Data Link Data Link Data LinkPhysical Physical Physical Physical Physical Each router provides its services to support upper layer functions

34. Layers 47:Transport, Session, Presentation, andApplication Layers

35. Transport Layer Segments upper-layer applications Establishes an end-to-end connection Optionally, ensures data reliability

36. Transport LayerSegments Upper-Layer ApplicationsApplication Electronic File TerminalPresentation Mail Transfer SessionSession Transport Application Application Data Data Port Port Segments

37. Transport Layer Establishes ConnectionSender Receiver Synchronize Negotiate Connection Synchronize Acknowledge Connection Established Data Transfer (Send Segments)

38. Transport LayerSends Segments with Flow Control Transmit Sender Receiver Buffer Full Not Ready Stop Process Segments Go Ready Buffer OK Resume Transmission

39. 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

40. Transport LayerAn 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

41. Transport to Network Layer End-to-End Segments Routed Packets

42. 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

43. Session Layer In networking a session is a semi-permanent interactive information interchanges, a communication or a meeting between two or more communicating devices, or between a computer and a user (Login Session). A session begins when an application wants to make connection to a remote server, the session layer opens a temporary channel between the two. A session is established at a certain point in time and torn down at a later point in time. There could be more than one session at the same time. The session layer can time stamp data. So that it knows where to re-start the transfer.

44. Presentation Layer Text Graphics Data Visual images ASCII PICTlogin: EBCDIC TIFF Encrypted JPEG Sound GIF MIDI Video MPEG QuickTime Provides code formatting and conversion for applications

45. Presentation Layer ASCII : American Standard Code for Information Interchange. EBCDIC: Extended Binary Coded Decimal Interchange Code. JPEG : Joint Picture Expert Group. TIFF : Tagged Image File Format. GIF : Graphical Image Format. BMP : Bitmap Image. MPEG : Motion Picture Expert Group. AVI : Audio Video Interleave. WAV : Windows Audio Video

46. Application Layer COMPUTER APPLICATIONS NETWORK Word Processor APPLICATIONS INTERNETWORK Presentation Graphics Electronic Mail APPLICATIONS File Transfer Electronic Data Interchange Spreadsheet Remote Access World Wide Web Database Client-Server Process E-Mail Gateways Design/Manufacturing Information Location Special-Interest Bulletin Boards Project Planning Network Management Financial Transaction Services Others Others Internet Navigation Utilities Conferencing (Voice, Video, Data) Internetwork applications Others can extend beyond the enterprise (i.e., to suppliers, etc.)

47. Summary OSI reference model describes building blocks of functions for program-to- program communications between similar or dissimilar hosts Layers 47 (host layers) provide accurate data delivery between computers Layers 13 (media layers) control physical delivery of data over the network