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The ISO/OSI Reference Model

The ISO/OSI Reference Model. The Model Functionality of Layers Example Networks. The OSI Model. Basic principles of layered architecture: Each layer means different layer of abstraction Each layer should perform a well defined function

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The ISO/OSI Reference Model

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  1. The ISO/OSI Reference Model The Model Functionality of Layers Example Networks

  2. The OSI Model • Basic principles of layered architecture: • Each layer means different layer of abstraction • Each layer should perform a well defined function • The functions of layer should promote standardization • The information flow across the interfaces should be minimized • The number of layers should be large enough to separate functionality and small enough to keep the architecture under control

  3. The OSI Model • Introduced in 1983 • The OSI model has seven layers • The OSI model is not a network architecture • It does not specify the exact services ant protocols • It specifies what kind of functions each layer should perform • ISO has produced standards for each layer as separate documents • Good model to study networking concepts

  4. The OSI reference model Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum

  5. The Physical Layer • Transmission of raw bits over communication channel • Transmission media, its physical properties • Magnetic media • Twisted pair • Coaxial cable • Fiber optics • Wireless transmission • Data rate of communication channel

  6. The Data Link Layer • Providing error-free transmission line for upper layers between two adjacent nodes • Breaking information into frames and using services of physical layer • Error-detecting codes • Error-correcting codes • Ensuring uniqueness and correctness of frames • Flow control between sender and receiver • Access to shared communication channel

  7. The Network Layer • Routing of data packets from source host to destination host • Controlling network congestion • Accounting of network traffic • Internetworking - interconnection of multiple heterogeneous networks • Addressing issues • Packet sizes • Protocol differences

  8. The Transport Layer • Transmission of data between software entities on end-point hosts • Providing channel for each application, mapping channels to Network Layer connection • Ensuring uniqueness and correctness transmitted of data units • Quality of Service (QoS) management • Connection management, naming • Flow control and buffering

  9. The Session Layer • Establishment of sessions between applications • Enhancing Transport Layer services • Dialogue control: directions, etc. • Token management • Synchronization: checkpoints

  10. The Presentation Layer • Providing general solutions to syntax and semantics transmitted data • Encoding of data “on the wire” into intermediate format • Compression of data • Encryption of data

  11. The Application Layer • All the network application software • Network virtual terminals • File transmission • Electronic mail • File servers • Database servers • Application servers • Object servers • Transaction servers

  12. Data Transmission in OSI model Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum

  13. The TCP/IP Reference Model Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum

  14. Initial TCP/IP protocols Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum

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