Lecture 03
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This document discusses the OSI model and its 7 layers. It describes the layered architecture approach of breaking communication tasks into simpler sub-tasks handled by individual layers. Each layer provides services to the layer above and relies on the layer below. The layers are the physical, data link, network, transport, session, presentation, and application layers. Each layer has specific responsibilities for handling data transmission and communication functions.
Lecture 03
- 2. Need of a Layered Architecture OSI Model 7 Layers of OSI Model Functional Details of OSI Layers • Physical Layer • Data Link Layer • Network Layer • Transport Layer • Session Layer • Presentation Layer • Application Layer
- 3. Layered Architecture Design Philosophy of Layered Architecture The complex task of communication is broken into simpler sub- tasks or modules Each layer performs a subset of the required communication functions Each layer relies on the next lower layer to perform more primitive functions Each layer provides services to the next higher layer Changes in one layer should not require changes in other layers Helps in troubleshooting and identifying the problem
- 4. An example Sending a letter
- 5. OSI Model To standardize the design of communication system, the ISO created the OSI model. Open Systems Interconnection Open System: A model that allows two different systems to communicate regardless of their underlying network Purpose of the OSI MODEL Open Communication between different systems without requiring changes to the hardware and software.
- 6. OSI MODEL Definition of OSI Model A layered framework for the design of network systems that allows communication across all types of computer systems regardless of their underlying architecture. Each layer performs a subset of the required communication functions Each layer relies on the next lower layer to perform more primitive functions Each layer provides services to the next higher layer Changes in one layer should not require changes in other layers
- 7. OSI MODEL Layers of the OSI Model 1. Physical (Bits) 2. Data Link (Frames) 3. Network (Packets) 4. Transport (Segment) 5. Session (Dialog units) 6. Presentation (Raw Data) 7. Application (Text, Numbers)
- 8. Interfaces between Layers The passing of the data and network information down through the layers of the sending device and back up through the layers of the receiving device is made possible by an interface between each pair of adjacent layers.
- 9. Organization of layers The layers are divided into two groups Network support layers: Deals with physical aspects of moving from one device to another. Layers 1,2,3 User Support layers Allow interoperability among unrelated software systems. Layers 5,6,7 Layer 4 links the two subgroups what the lower layers have transmitted in form that upper layer can use. The upper OSI are always implemented in software lower layers are combination of hardware and software. Except for the physical layer which is mostly hardware.
- 10. An exchange using the OSI model
- 11. Physical layer
- 12. Physical layer responsibilities The physical layer is responsible for transmitting individual bits from one node to the next. Characterises of Media: The physical layer defines the charactertics and type of transmission medium. Representation of bits: The physical layer data consists of a stream of bits(sequence of 0,s and 1,s) with no interpretation. To be transmitted, bits must be encoded into signals-electrical or optical. The physical layer defines the type of encoding. Data Rate: The transmission rate- the number if bits sent each second is also defined by the physical layer. Line configuration: The physical layer defines the attachment of devices with medium Transmission Mode: The physical layer also defines the direction of transmission between two devices: simplex, half duplex,full duplex
- 13. Data link layer
- 14. Data link layer responsibilities The data link layer is responsible for moving frames from one hop (node) to the next.
- 15. Example 1
- 16. Network Layer
- 17. Network Layer responsibilities The network layer is responsible for the delivery of individual packets from the source host to the destination host .
- 20. Transport Layer responsibilities The transport layer is responsible for the delivery of a message from one process to another.
- 22. Session Layer
- 23. Session Layer responsibilities The session layer is responsible for dialog control and synchronization.
- 25. Presentation Layer responsibilities The presentation layer is responsible for translation, compression, and encryption.
- 27. Application Layer responsibilities The application layer is responsible for providing services to the user. Network virtual terminal (Remote log-in) File transfer and access Mail services Accessing the World Wide Web
Editor's Notes
- #6: OSI Model is not a Protocol. It is a model for understanding and designing a network architecture that is flexible, robust and interoperable