1. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas The ISO/OSI Reference Model The Model Functionality of Layers Example Networks

2. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas 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. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas 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. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum The OSI reference model

5. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas 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. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas 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. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas 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. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas 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. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas The Session Layer Establishment of sessions between applications Enhancing Transport Layer services Dialogue control: directions, etc. Token management Synchronization: checkpoints

10. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas 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. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas 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. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum Data Transmission in OSI model

13. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum The TCP/IP Reference Model

14. Microcomputer Networking II St. Cloud State University MCS 426, Fall 1999 Instructor: Adomas Svirskas Figure from book Computer Networks 3rd ed., by A.S. Tanenbaum Initial TCP/IP protocols