OSI Reference Model & Layered Communication

1. OSI Reference Model & Layered Communication Sritrusta Sukaridhoto

2. OSI Layer • Open Systems Interconnection for Communications • There are 7 Layers • Layers 7,6,5 are oriented more toward services to the applications • Layer 4,3,2,1 are oriented more toward the flows data from end-to-end through network

3. 7 Layer OSI

4. How to Remember (CISCO) • Please  Physical • Do  Data Link • Not  Network • Throw  Transport • Sousces  Session • Pizza  Presentation • Away  Application

5. Application Layer 7

6. Function & Description • An application that communicates with other computers is implementing OSI application layer concepts. Application layer refer to communications service to application.

7. Example • Telnet • HTTP • FTP • WWW Browser • NFS • SMTP Gateway • SNMP

8. Presentation Layer 6

9. Function & Description • This layer main purpose is defining data format such as ASCII text, EBCDIC text, binary, BCD, JPEG. • Encryption is also defined by OSI as presentation layer service.

10. Example • JPEG • ASCII • TIFF • GIF • PICT • MPEG • MIDI • Encryption

11. Session Layer 5

12. Function & Description • This session layer defines how to start, control, and end conversation (called session). • This includes the control and management of multi bidirectional messages so that application can be notified if only some of a series of messages are completed.

13. Example • RPC • SQL • NFS • Netbios Names • AppleTalk • ASP • SCP • DECnet

14. Transport Layer 4

15. Function & Description • Layer 4 includes the choice of protocols that either do or do not provide error recovery. Multiplexing of incoming data for different flows to applications on the same host.

16. Example • TCP • UDP • SPX

17. Network Layer 3

18. Function & Description • This layer defines end-to-end delivery packets. To accomplish this, the network layer defines logical addressing so that any endpoint can be identified. It also defines how routing works and how routes are learned so that the packets can be delivered • Network layer also defines how to fragment a packet into smaller packets to accommodate media with smaller maximum transmission unit size

19. Example • IP • IPX • AppleTalk DDP

20. Data Link Layer 2

21. Function & Description • The data link specifications are concerned with getting data across one particular link or medium. The data link protocols define delivery across an individual link. These protocols are necessary concerned with the type of media in question.

22. Example • IEEE 802.3/802.2 • HDLC • Frame Relay • PPP • FDDI • ATM

23. Physical Layer 1

24. Function & Description • Deal with the physical characteristics of the transmission medium, Connection pins, use of pins, electrical currents, encoding and light modulation.

25. Example • Ethernet • RJ-45 • V.35 • FDDI • EIA/TIA-232

26. Some protocol define details of multiple layers. • Example: NFS

27. Benefit & Concept • Humans can discuss and learn about many details of a protocol specification easier • Standardized interfaces among layers • Better environment for interoperability • Reduce complexity, faster production • Each layer can define header and trailers around the user data • One layer use the services of the layer immediately below it.

28. Interaction Between OSI Layer

29. On Same Computer

30. Step 1 = Physical Layer, ensure bit synchronization • Step 2 = Data Link Layer, Frame Check Sequence (FCS) whether error occurred in transmission • Step 3 = Network Layer, Exam address • Step 4 = Transport Layer, acknowleadment • Step 5 = Session Layer, to ensure that a series of messages is completed • Step 6 = Presentation Layer, manipulate data format • Step 7 = Application Layer, processes the final header and then can examine the true end-user data

31. Different Computer

32. Data Encapsulation

33. 5 Step Data Encapsulation • Create the data • Package the data for transport • Add the destination network layer address to the data • Add the destination data link address to the data • Transmit the bit

34. Frames, Packets and Seqments

35. The layer 2 PDU (Protocol Data Unit) including the data link header and trailer = Frame • The Layer 3 PDU = packet • The Layer 4 PDU = seqment

36. OSI, TCP/IP

37. OSI Transport Layer Function • Connection Oriented vs Connectionless Oriented

38. Error Recovery

41. Flow Control • Flow control is the process of controlling the rate at witch a computer sends data. • Implementation: • Buffering • Congestion Avoidance • Windowing

42. Buffering • Buffering simply means that computers reserve enough buffer space that bursts of incoming data can be held until processed

43. Congestion Avoidance

44. Windowing

45. Data Link Function • MAC = Media Access Control • CSMA/CD = Carrier Sense Multiple Access/Collision Detect

46. OSI Network Layer Function • Routing • Sending data to a nearby Router • Routing data Across Network • Delivering Data to End Destination • Addressing

48. Summary • Application (Layer 7)  User Interface  Telnet, HTTP • Application (Layer 6)  How data is presented  JPEG, ASCII • Session (Layer 5)  Keeping data separate from different application  OS, application access scheduling • Transport (Layer 4)  Reliable or unreliable delivery, Multiplexing  TCP, UDP, SPX • Network (Layer 3)  Logical addressing, Routing  IP, IPX • Data Link (Layer 2)  MAC, error detection  802.3/802.2, HDLC • Physical (Layer 1)  Devices  Ethernet, V.35