OSI Reerence Model


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OSI Reerence Model

  1. 1. © N. Ganesan, Ph.D. , All rights reserved. Chapter OSI Reference Model
  2. 2. ISO and OSI Defined • ISO – International Standards Organization • OSI – Open Systems Interconnect/interface
  3. 3. OSI Model Background • OSI model Introduced in 1978 and revised in 1984 by ISO • It is first standardization of protocol of N/W. • It is also called OSI because it connect open system. • Open system means a system that is open for communication with other system.
  4. 4. OSI Model Background • It give set of rules , how to different n/w communicate with each other. • It used layered approach because it divide work and assign work to each layer. • Protocol is used to implement specific task. • Protocol is set of rules.
  5. 5. OSI Model Background • OSI model is called reference model because it provide reference to implement network communication. • It tell just what each layer should do. • OSI is not a physical model, it is set of guideline that application developer can use to create and implement applications that can run on network.
  6. 6. The Layered Approach to Communication 7. Application 6. Presentation 5. Session 4. Transport 3. Network 2. Data Link 1. Physical
  7. 7. Division of Layers Upper Layers Lower Layers Middle Layer 7. Application 6. Presentation 5. Session 4. Transport 3. Network 2. Data Link 1. Physical
  8. 8. The Function of a Layer • Each layer deals with one aspect of networking – Ex. Layer 1 deals with the communication media • Each layer communicates with the adjacent layers – In both directions – Ex: Network layer communicates with: • Transport layer • Data Link layer • Each layer formats the data packet – Ex: Adds or remove header
  9. 9. Role of Layers 7. Application 6. Presentation 1. Physical Node A Data Out Data In To/from Node B
  10. 10. The Role of Layers in Point-to- point Communication 7. Application 1. Physical 7. Application 1.Physical Node a Node b
  11. 11. 7. Application Layer function • This layer provide user interface and support services. • It allow user to direct access to application and n/w services. • Services include web service(HTTP), mail service(SMTP,POP3, IMAP), telnet services(remote login), file service(FTP, TFTP)
  12. 12. 6. Presentation Layer function • Data formatting is done by this layer • Presentation layer is responsible for data encoding/decoding, encryption/decryption, compression/decompression • It is also responsible for user authentication • It is also responsible for translation services
  13. 13. 5. Session Layer Function • Session layer is dialog controller. • Session layer establish, maintain, and terminate session between two systems. • It is also provide synchronization service. • Session layer decide transmission type like.. Simplex, half-duplex, full duplex.
  14. 14. 4. Transport Layer Function • It provide transport( transport provider). • It provide end to end connection via virtual circuit. • It is responsible for connection less and connection oriented communication. • It is also responsible for error detection, error correction(data recovery), flow control.
  15. 15. 4. Transport Layer Function • Message is divided into transmittable segment and reassemble. • Connection oriented communication is reliable, secure and provide ack. Ex. TCP • Connection less communication is not reliable, secure and does not provide ack. Ex.UDP
  16. 16. 3. Network Layer Function • This layer is responsible for routing. • Routing means communication between different network. • It provide logical addressing which router use for path determination. • Using IP, it manage device addressing, track the address of the devices on the network and determine the best path to data transfer. • It is also responsible for IP to MAC and Mac to IP Mapping.
  17. 17. 2. Data Link Layer Function • Data link layer is responsible for taking packet from network layer and put it on network media . • It convert packet into frame and vise versa. • Data link layer has two sub layers. 1). Logic link control.(LLC) 2). Media access layer(MAC).
  18. 18. Data Link Layer Subdivision • Logical Link Control (LLC) work on IP – It identify network layer protocol and tells what to do once frame received. – Error and flow control • Media Access Control (MAC) work on MAC – It provide access to media using Mac address. – It define how to put frame on the media. – Error detection and error correction , flow control.
  19. 19. 1. Physical Layer Function • It is responsible for transmit bits over media. – Carry data from the h higher layers • It define following characteristics. – Electrical – Mechanical – Functional – Example: specify voltage, pin out of cable.
  20. 20. Media Access Control Application • Network Interface Card driver NETWORK SOFTWARE NETWORK CARD NIC Driver facilitates data transfer
  21. 21. Summary of layers
  22. 22. Layer Operations • At each layer, additional information is added to the data packet • An example would be information related to the IP protocol that is added at Layer 3
  23. 23. Formatting of Data Through the Layers Application Header Presentation Header Session Header Transport HeaderNetwork Header Data Link Header and Trailer Physical Frame Preamble
  24. 24. Data formatting
  25. 25. Packet : General Format Header Trailer Data A general concept of packets serves as a prerequisite to the understanding of the ISO-OSI model.
  26. 26. Some Header Information Added at Various Layers • Packet arrival information • Receiver’s address • Sender’s address • Synchronization character
  27. 27. Data • Actual data • May contain error correction code – Performed on individual characters of the data – Example: Parity • Size may vary – Depending on the protocol – Example • 802.3 specifies range of data packet length
  28. 28. Tasks involved in sending letter
  29. 29. 7 Layers 7. Application Layer 6. Presentation Layer 5. Session Layer 4. Transport Layer 3. Network Layer 2. Data Link Layer 1. Physical Layer All People Seem To Need Data Processing
  30. 30. How Does It All Work Together • Each layer contains a Protocol Data Unit (PDU) – PDU’s are used for peer-to-peer contact between corresponding layers. – Data is handled by the top three layers, then Segmented by the Transport layer. – The Network layer places it into packets and the Data Link frames the packets for transmission. – Physical layer converts it to bits and sends it out over the media. – The receiving computer reverses the process using the information contained in the PDU. 2
  31. 31. Layer 7 Application All user access and net services Layer 6 Presentation People data formatting Layer 5 Session Seem Dialogues controller Layer 4 Transport To Computer Segment TCP and UDP,IPX end to end transport ation and Quality of Servic Layer 3 Network Need Router, brouter, layer 3 switch Packet Routable Protocols. (IP, IPX, AppleTalk) routing protocol(rip, igrp) IGMP ICMP, ARP, RARP ip addressind Path Selection, routing Data Protocols Words to Remember OSI Model Layer Pneumonic devices OSI Model layer and har Layer 1 Physical Processing Repeater, Hub (Multi-port), Cabling Bit Layer 2 Data Bridge (2 Ports) or Switch and NIC, intelligent hub Frame Data Link -MAC -LLC protocol defined by underlying network bit transmission over media Computer Data FTP, Telnet, SMTP, SNMP, DNS making bits to frame and host to host delievery protocol defined by underlying network