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The OSI Model

The OSI Model. By: Sushant Kumar www.sushantkumar.wordpress.com. Brief History. Introduced in late 1970s. What is OSI model ?. Set of protocols Allows two different systems to communicate Regardless of underlying architecture. OSI model is not a protocol.

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The OSI Model

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  1. The OSI Model By: Sushant Kumar www.sushantkumar.wordpress.com

  2. Brief History • Introduced in late 1970s

  3. What is OSI model ? • Set of protocols • Allows two different systems to communicate • Regardless of underlying architecture

  4. OSI model is not a protocol • Model for understanding network architecture • Flexible • Robust • Interoperable

  5. Layers (PDNTSPA) • Application • Presentation • Session • Transport • Network • Data Link • Physical

  6. Physical Layer • Char of interface and medium • Type of transmission medium • Representation of bits • Type of encoding • How 0s &1s are changed to signals • Data Rate • Synch of Bits • Clocks of sender & receiver must be in synch

  7. Physical Layer… • Line configuration • Point 2 point or multipoint • Topology • Transmission mode • Simplex, half-duplex, full-duplex

  8. Data Link layer • Transforms physical layer into a reliable link • Framing • Divides data in frames • Physical addressing • Adds a header to the frame • Flow control • If the receiver cannot receive data at the rate at which sender is ending data

  9. Data Link layer… • Access control • When 2 devices have the same link, data link layer protocols decide which device gets the control

  10. Network Layer • Responsible for source 2 destination delivery of a packet across multiple links • Needed when 2 systems are connected 2 different networks

  11. Network Layer… • Logical addressing • Adds header 2 the packet coming from upper layer • Used when 2 different networks are there • Routing • Packet has 2 be routed/switched to multiple destinations

  12. Transport Layer • Responsible for process to process delivery of the packets • Network layer treats a packet individually

  13. Transport Layer… • Service-point addressing • Computer has several processes running • Delivery from a specific process on one computer to another specific process • Segmentation & Re-assembly • Message is divided into transmittable segments • Connection control • Transport layer can be • Connection oriented • Connectionless

  14. Transport Layer… • Flow control • Flow control is end 2 end, rather on a single link • Error Control • This is process to process rather than a single link • Makes sure the entire message has arrived

  15. Session Layer • Synchronizes the interaction among communicating systems

  16. Session Layer… • Dialog Control • Allows two systems to enter into a dialog • Communication takes place in either half-duplex or full-duplex mode • Synchronization • Allows a process to add checkpoints after a certain amount of data is sent

  17. Presentation Layer • Concerned with syntax and semantics of information sent

  18. Presentation Layer… • Translation • Changes the information into a common format • Encryption • Compression

  19. Application Layer • Enables user to access network

  20. Application Layer… • Network Virtual Terminal (NVT) • User to log-on to remote host • File transfer, access and management • Mail services • Directory services

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