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  • 1. Unit03: The OSI Model
  • 2. Overview • Open Systems Interconnection • Encapsulation • Physical • Data-link • Network • Transport • Session • Presentation • Application
  • 3. Open Systems Interconnection • Proposed by the International Organization for Standardization (IOS) and released in 1984 • Decidedly structured set of seven protocol layers interconnecting as a stack • Developed to maintain the ability to connect diverse types of computers • Valuable as a teaching and development tool
  • 4. OSI
  • 5. Encapsulation The sending station converts data into increasingly smaller capsules until they are mere bits Puts those bits back together into increasingly larger capsules at the receiving station
  • 6. Physical Layer • Transmission of raw data in the form of a stream of bits across physical media • Physical Layer conveys the bit stream data through electrical impulses, light, or radio signals • The connections that are supported at the physical layer are either multipoint or point-to-point
  • 7. Physical Layer
  • 8. Data Link Layer • It is the only layer with two sublayers: Media Access Control (MAC) and Logical Link Control (LLC). • The data-link layer supplies hardware addresses, identifies errors, and manages flow control. • Bit stream received from the physical layer is assembled into larger pieces, called frames • Able to insert control information into a frame header • Source and destination of the frame on that network segment
  • 9. Data Link Layer • Media Access Control (MAC) – This sublayer defines how devices are able to gain access to the media – maintains the hardware address for the device • The three types of MACs are: – Contention – Polling – Token passing
  • 10. Data Link Layer • MAC Address – also called the hardware address – MAC address is unique to each interface
  • 11. Data Link Layer • Logical Link Control – second data-link sublayer – Responsible for logical link functions of single or multiple connections – LLC provides services to the higher-level network layer – The LLC primarily provides flow control and frame sequencing services
  • 12. Network Layer • Providing an address for each network segment • Providing a logical address for each device that is separate from the MAC address • Routing and forwarding data • Selecting a route if there are multiple routes to the same network segment • Discovering the routes to other network segments • Error handling, congestion control, and packet sequencing
  • 13. Network Layer
  • 14. Network Layer • RIP – Distance Vector routing protocols periodically broadcast the entire routing table to neighboring routers • OSPF – These advanced protocols use a hello process to announce a new router on the network – the time it takes for the new routes to be added to the network is greatly reduced
  • 15. Transport Layer • Provides for a transparent transfer of data between the sender and receiver nodes • Control information provides end-to-end recovery and flow control • Ensures that the data is completely transferred
  • 16. Transport Layer • Connection Orientation – Connection-oriented • TCP • Reliable Transfer • use of acknowledgments (ACK) – Connectionless • UDP • Does not use ACK • Smaller headers and less time needed
  • 17. Session Layer • Establishes a connection between applications and manages that connection until it terminates. • Also terminate a session in an orderly manner • Remote procedure calls (RPCs) function at the session layer • Example : Telnet and Citrix MetaFrame ICA sessions • Data is transmitted in a session in three ways – Simplex. – Half-duplex.. – Full-duplex.
  • 18. Presentation Layer • Provides the way for data to be presented to the application • Encryption/decryption and data compression/expansion are handled at this layer • provide formatting data • Bit order • Byte order • Character code • File syntax.
  • 19. Application Layer • Supports end-user processes • Specific to the application being used. • Application-layer protocols connect across the internetwork in three ways – Collaborative computing – Operating system call interception – Remote operation