THE COMPLETE OSI MODEL
- 1. OSI Reference ModelOSI Reference Model By:- F.Y. B.Sc. I.T. (A) Group no:-007
- 2. Submitted by: Aman Gupta Asmita Gupta Dolly Jadhav Amit Gupta Sourabh Gupta Navnath Jadhav Ashish Gupta Chetana Ingale Rohit Jadhav Guided by: Prof. S. Dengane OSI MODEL
- 3. 3 Objectives Data communication among heterogeneous systems – difficulties and solutions The need for layered architecture Design issues for the layers The OSI model
- 4. 4 Network complexities Different types of hardware and software Different operating systems Different types of data to be transferred – text, images, music, video, etc Data must be transferred without errors Many different paths may have to be taken Yet computers must communicate with each other in a network
- 5. 5 How to Reduce this complexity Recall concepts of functions, data hiding, passing values to as function, getting results from a function How the function works is not important – what inputs it requires and what outputs it produces are important “Black box” approach – services provided are known but the details are hidden
- 6. 6 What is a protocol? It is a formal description of message formats and the rules that two computers must follow in order to exchange messages. This set of rules describes how data is transmitted over a network.
- 7. 7 Why are protocols needed? Protocols are needed for communication between any two devices. In what format will the messages be transmitted? At what speed should messages be transmitted? What to do if errors take place? What to do if parts of a message are lost?
- 8. 8 Open Systems Interconnect (OSI) Model Who made: International Standards Organization (ISO) A Model of How Protocols and Networking Components Could be Made “Open” means the concepts are non-proprietary; can be used by anyone. OSI is not a protocol. It is a model for understanding and designing a network architecture that is flexible and robust.
- 9. 9 Open Systems Interconnect (OSI) Model The OSI model describes how data flows from one computer, through a network to another computer The OSI model divides the tasks involved with moving information between networked computers into 7 smaller, more manageable sub-task . A task is then assigned to each of the seven OSI layers. Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently.
- 10. 11 7-layer OSI model Why so many layers? To reduce complexity, networks are organized as a stack of layers, one below the other Each layer performs a specific task. It provides services to an adjacent layer This is similar to the concept of a function in programming languages – function does a specific task
- 12. 13 Layered Approach The entities comprising the corresponding layers on different machines are called peers It is the peers that communicate by using the protocols Actually, data is not transferred from layer n on one machine to layer n on another machine Each layer passes data and control information to the layer immediately below it, until the lowest layer is reached Actual data communication takes place through the lowest layer – the physical layer
- 13. 14 Design Issues for the Layers Addressing Error control Order of messages must be preserved Flow control – fast sender and slow receiver ! Disassembling, transmitting, and reassembling large messages Multiplexing / de-multiplexing Routing
- 14. 15 Concept of Protocols A protocol is a set of rules governing the format and meaning of the packets Protocols relate to packets sent between peer entities on different machines Entities use protocols Protocols can be changed provided the services visible to the user do not change. Thus services and protocols are completely decoupled
- 15. 16 The Layers of the OSI Model Application Presentation Session Transport Network Data Link Physical
- 16. 17 The Layers of the OSI Model Some Mnemonics Application Presentation Session Transport Network Data Link Physical All People Seem To Need Data Processing Please Do Not Tell Secret Passwords Anytime
- 17. 18 Physical layer • Specifications for the physical components of the network. • Functions of Physical Layer: • Bit representation – encode bits into electrical or optical signals • Transmission rate – The number of bits sent each second • Physical characteristics of transmission media • Synchronizing the sender and receiver clocks • Transmission mode – simplex, half-duplex, full duplex • Physical Topology – how devices are connected – ring, star, mesh, bus topology Application Presentation Session Transport Network Data Link Physical
- 19. 20 Data Link Layer Responsible for delivery of data between two systems on the same network Main functions of this layer are: • Framing – divides the stream of bits received from network layer into manageable data units called frames. • Physical Addressing – Add a header to the frame to define the physical address of the source and the destination machines. • Flow control – Impose a flow control – control rate at which data is transmitted so as not to flood the receiver (Feedback-based flow control) • Error Control – Adds mechanisms to detect and retransmit damaged or lost frames. This is achieved by adding a trailer to the end of a frame Application Presentation Session Transport Network Data Link Physical
- 21. 22 Network Layer Main functions of this layer are: • Responsible for delivery of packets across multiple networks • Routing – Provide mechanisms to transmit data over independent networks that are linked together. • Network layer is responsible only for delivery of individual packets and it does not recognize any relationship between those packets Application Presentation Session Transport Network Data Link Physical
- 22. 23 Network Layer
- 23. 24 Transport Layer Main functions of this layer are: • Responsible for source-to-destination delivery of the entire message • Segmentation and reassembly – divide message into smaller segments, number them and transmit. Reassemble these messages at the receiving end. • Error control – make sure that the entire message arrives without errors – else retransmit. Application Presentation Session Transport Network Data Link Physical
- 25. 26 Session Layer Main functions of this layer are: • Dialog control – allows two systems to enter into a dialog, keep a track of whose turn it is to transmit • Synchronization – adds check points (synchronization points) into stream of data. Application Presentation Session Transport Network Data Link Physical
- 26. 27 Session Layer H5 syn syn syn From Presentation Layer To Transport Layer Session Layer From Transport Layer To Presentation Layer H5 syn syn syn Session Layer
- 27. 28 Presentation Layer Responsibilities of this layer are: • Translation • Different computers use different encoding systems (bit order translation) • Convert data into a common format before transmitting. • Syntax represents info such as character codes - how many bits to represent data – 8 or 7 bits • Compression – reduce number of bits to be transmitted Application Presentation Session Transport Network Data Link Physical
- 28. 29 Presentation Layer • Encryption – transform data into an unintelligible format at the sending end for data security • Decryption – at the receiving end Application Presentation Session Transport Network Data Link Physical
- 29. 30 Application Layer •Contains protocols that allow the users to access the network (FTP, HTTP, SMTP, etc) • Does not include application programs such as email, browsers, word processing applications, etc. • Protocols contain utilities and network- based services that support email via SMTP, Internet access via HTTP, file transfer via FTP, etc Application Presentation Session Transport Network Data Link Physical
- 30. 31 Application Layer To Presentation Layer From Presentation Layer
- 31. 32 Summary of Functions of Layers Application Presentation Session Transport Network Data Link Physical To allow access to network resources To establish, manage & terminate sessions To move packets from source to destination To transmit bits over a medium & provide electrical specs. To translate, encrypt and compress data To provide reliable end-to-end message delivery To organise bits into frames
- 32. 33 References Katre J.S, June 2013, Computer Networks, Pune, pp 1.63-1.75. Prof. Joshi Jayshri, January 2015, Telecommunication switching systems, Pune, pp 5.24-5.31. https://en.wikipedia.org/wiki/OSI_model. https://www.techopedia.com/2/27094/networks/an- introduction-to-the-osi-model. http://faculty.spokanefalls.edu/Rudlock/files/WP_Simoneau_ OSIModel.pdf. http://computernetworkingnotes.com/osi-layer- modals/advantage-of-osi-layer.html. https://support.microsoft.com/en-us/kb/103884.
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Editor's Notes
- #15: Addressing – specify with which machine to communicate Error detecting and error correcting codes can be used provided same mechanism is being used at both ends Order of messages must be preserved. Messages may arrive out of order – i.e. not in the sequence. The protocol must allow the receiver to reassemble the pices properly, in the required sequence. Flow control – A fast sender should not swamp a slow receiver. Some kind of feedback is required between sender and receiver in order to limit the data transfer rate. Arbitrarily long messages must be broken down into smaller messages. These small messages are then transmitted and reassembled at the receiving end. Multiplexing/de-multiplexing – use a single connection for multiple, unrelated conversations Routing – if multiple paths exist between source and destination, which path to use. Various factors may come into play – urgency, speed, volume of data, etc.
- #19: 1. This layer is concerned with issues such as signal durations, voltage levels (what voltage represents a 0 and what represents a 1), types of connectors, assignment of pins on connectors