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OSI Model


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Introduction to OSI Design
Issues in OSI
OSI Standard
OSI Protocol
OSI Layer Function & Data Control

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OSI Model

  1. 1. MTN 2013Computer Network Technology Chapter 3 OSI Model
  2. 2. Outline1. Introduction to OSI Design2. Issues in OSI3. OSI Standard4. OSI Protocol5. OSI Layer Function & Data Control11/17/2011 MTN 2013 2
  3. 3. 1. Introduction to OSI Design• Open Systems Interconnected Model – was created in the 70’s by the ISO (International Organization for Standardization) • Several different people got together and considered all functions of communications – The concept of a 7 layer model was provided by the work of Charles Bachman, Honeywell Information Services. – Various aspects of OSI design evolved from experiences with the ARPANET – Integrated Services Digital Network (ISDN) was a big factor – 7 layers = 4 upper and 3 lower11/17/2011 MTN 2013 3
  4. 4. OSI Model• OSI Model – Model for understanding and developing computer-to- computer communication – Divides network architecture into seven layers – Modular approach – Ensures error free delivery – Defines functionality NOT services or protocols• Network Architect – Designs networks• Network Administrators – Need to understand11/17/2011 MTN 2013 4
  5. 5. OSI Reference Model in Practice• The OSI reference model is used in many ways: – To provide assistance when troubleshooting network problems – To provide a common terminology and framework for networking technology developers – To facilitate the development of connectivity standards needed for flexible open architectures – To enable the development of protocol stacks that allow network nodes to communicate with one another11/17/2011 MTN 2013 5
  6. 6. Seven Layers of Network Architecture ALL PEOPLE SEEM TO NEED DATA PROCESSING FIGURE : OSI Model11/17/2011 MTN 2013 6
  7. 7. 2. Issues in OSISr. No. TCP/IP Reference Model OSI Reference Model Defined after the advent of1 Defined before advent of internet Internet Service interface and protocols Service interface and protocols are clearly2 were not clearly distinguished distinguished before3 TCP/IP supports Internet working Internet working not supported4 Loosely layered Strict layering5 Protocol Dependent standard Protocol independent standard6 More Credible Less Credible TCP reliably delivers packets, IP7 All packets are reliably delivered does not reliably deliver packets11/17/2011 MTN 2013 7
  8. 8. 3. OSI Standard• Was created because people realized that our computers needed to talk to each other(and there was no one dominant computer system)• Consist of different technologies – hardware and software• i.e each computer vendor, had a different hardware design, OS and a proprietary protocol to enable communication between two computers of the same make.• Need one standard protocol to define the functionality11/17/2011 MTN 2013 8
  9. 9. 4. OSI Protocol• It is a way of sub-dividing a communications system into smaller parts called layers.• Similar communication functions are grouped into logical layers.• A layer provides services to its upper layer while receiving services from the layer below.• On each layer, an instance provides service to the instances at the layer above and requests service from the layer below11/17/2011 MTN 2013 9
  10. 10. 5. OSI Layer Function & Data Control• 7 layers 1. Physical 2. Data link 3. Network 4. Transport 5. Session 6. Presentation 7. Application11/17/2011 MTN 2013 10
  11. 11. OSI Reference Model: Layer 1 Transmits and receives raw data to communication medium. Does not care about contents. voltage levels, speed, connectors1 Physical Examples: RS-232, 10BaseT11/17/2011 MTN 2013 11
  12. 12. OSI Reference Model: Layer 2 Detects and corrects errors. Organizes data into packets before passing it down. Sequences packets (if necessary). Accepts acknowledgements from receiver.2 Data Link1 Physical Examples: Ethernet MAC, PPP11/17/2011 MTN 2013 12
  13. 13. OSI Reference Model: Layer 3 Relay and route information to destination. Manage journey of packets and figure out intermediate hops (if needed).3 Network2 Data Link1 Physical Examples: IP, X.2511/17/2011 MTN 2013 13
  14. 14. OSI Reference Model: Layer 4 Provides a consistent interface for end-to-end (application-to- application) communication. Manages flow control. Network interface is similar to a4 Transport mailbox.3 Network2 Data Link1 Physical Examples: TCP, UDP11/17/2011 MTN 2013 14
  15. 15. OSI Reference Model: Layer 5 Services to coordinate dialogue and manage data exchange. Software implemented switch.5 Session Manage multiple logical4 Transport connections. Keep track of who is talking:3 Network establish & end communications.2 Data Link1 Physical Examples: HTTP 1.1, SSL, NetBIOS11/17/2011 MTN 2013 15
  16. 16. OSI Reference Model: Layer 6 Data representation6 Presentation Concerned with the5 Session meaning of data bits4 Transport Convert between machine representations3 Network2 Data Link1 Physical Examples: XDR, ASN.1, MIME, MIDI11/17/2011 MTN 2013 16
  17. 17. OSI Reference Model: Layer 77 Application Collection of application-specific protocols6 Presentation Provides interface to the software enabling programs to5 Session use network devices4 Transport3 Network Examples:2 Data Link email (SMTP, POP, IMAP) file transfer (FTP)1 Physical directory services (LDAP), browser,11/17/2011 MTN 2013 17
  18. 18. END Q&A11/17/2011 MTN 2013 18