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Layers Models

OSI Model. Layers Models. OSI Model. Layers Models. OSI MODEL TCP/IP MODEL. 7 Application. 6 Presentation. OSI MODEL INTRODUCTION. 5 Session. 4 Transport. 3 Network. 2 Data Link. 1 Physical. OSI Model. Open Systems Interconnection (OSI) Model.

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Layers Models

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  1. OSI Model Layers Models

  2. OSI Model Layers Models • OSI MODEL • TCP/IP MODEL

  3. 7 Application 6 Presentation OSI MODEL INTRODUCTION 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

  4. OSI Model Open Systems Interconnection (OSI) Model • International standard organization (ISO) established a committee in 1977 to develop an architecture for computer communication. • Open Systems Interconnection (OSI) reference model is the result of this effort. • In 1984, the Open Systems Interconnection (OSI) reference model was approved as an international standard for communications architecture. • Term “open” denotes the ability to connect any two systems which conform to the reference model and associated standards.

  5. OSI Model OSI Reference Model • The OSI model describes how information or data makes its way from application programmes through a network medium (such as wire) to another application programme located on another network. • The OSI reference model divides the problem of moving information between computers over a network medium into SEVEN smaller and more manageable problems . • This separation into smaller more manageable functions is known as layering.

  6. OSI Model OSI Reference Model: 7 Layers

  7. OSI Model OSI: A Layered Network Model • The process of breaking up the functions or tasks of networking into layers reduces complexity. • Each layer provides a service to the layer above it in the protocol specification. • Each layer communicates with the same layer’s software or hardware on other computers. • The lower 4 layers (transport, network, data link and physical —Layers 4, 3, 2, and 1) are concerned with the flow of data from end to end through the network. • The upper four layers of the OSI model (application, presentation and session—Layers 7, 6 and 5) are orientated more toward services to the applications. • Data is Encapsulated with the necessary protocol information as it moves down the layers before network transit.

  8. 7 Application NETWORK GOALS The two main benefits of networking computers are… 1.Communications Information can be distributed very quickly, such as email and video conferencing. 2. Saving Money Resources such as information, software, and hardware can be shared. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

  9. 7 Application NETWORK STRUCTURE Subnet Carries messages from host to host. Hosts End user machines or computers. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

  10. 7 Application NETWORK ARCHITECTURES A set of layers and protocols is called the network architecture. 1. Protocol Hierarchies Each layer offers services to the higher layers (interface). Interface – defines which request, response, and services the lower layer will offer to the upper layer. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

  11. Encapsulation • Data exists at each layer contained within a unit called a Protocol Data Unit (PDU). • The process by which data moves between PDU types is called Encapsulation • PDU move through interfaces between layers using Service Access Points (SAP)

  12. PDU’s And the OSI Model Encapsulation Decapsulation

  13. OSI Model protocols • The protocol defines set of rules that format of the data being exchanged, and the control and timing between layers.

  14. Protocol Reference Model of OSI II OSI Overview 1. OSI - layered framework for the design of network systems that allows communication across all types of computer systems. 2. The OSI 7 Layers. ( Brief functional overview. ) 3. Vertical and horizontal communication between the layers using interfaces. (defines what information and services should the layer provide to the layer above it. )

  15. Layers Each layer contains a logical grouping of functions Each function receive an input(one or more) and produces an output

  16. Protocol Reference Model of OSI 1. OSI – a standard, which allows communication between different systems without requiring changes to the logic of the underlying hardware and software.

  17. Protocol Reference Model of OSI Layer abstraction and the path of the message

  18. Protocol Reference Model of OSI OSI Overview 4. Data Encapsulation a) PDU conception – each protocol on the diff. layer has its own format. b) Headers are added while a packet is going down the stack at each layer. c) Trailers are usually added on the second layer.

  19. OSI Model Application Layer (Layer 7) • Application layer interacts with application programs and is the highest level of OSI model. • Application layer contains management functions to support distributed applications. • Examples of application layer are applications such as file transfer, electronic mail, remote login etc. • protocols: HTTP, FTP, SMTP • PUD: Data

  20. OSI Model OSI in Action • A message begins at the top application layer and moves down the OSI layers to the bottom physical layer. • As the message descends, each successive OSI model layer adds a header to it. • A header is layer-specific information that basically explains what functions the layer carried out. • Conversely, at the receiving end, headers are striped from the message as it travels up the corresponding layers.

  21. Presentation layer(Layer 6) • Coding and conversion of Application layer data to ensure that data from the source device can be interpreted by the application on the destination device. • Compression of the data in a manner that can be decompressed by the destination device. • Encryption of the data for transmission and the decryption of data upon receipt by the destination. • Examples: GIF, JPEG, TIFF, etc.

  22. Protocol Reference Model of OSI The OSI Layers 6. Presentation Layer • Translation(connects different computer systems) • Compression (transmission) • Encryption(security)

  23. Session layer(Layer 5) • Functions at this layer create and maintain dialogs between source and destination applications • Authentication • Permissions • Session Restoration (Checkpoint or recovery)

  24. Protocol Reference Model of OSI The OSI Layers 5. Session Layer • Session establishment, maintenance and termination (Deciding who sends, and when.) • Session support (security, name recognition, logging )

  25. Transport layer(Layer 4) • Tracking the individual communication between applications on the source and destination hosts • Segmenting data and managing each piece • Reassembling the segments into streams of application data • Identifying the different applications • Conversation Multiplexing • Segments • Connection-oriented conversations • Reliable delivery • Ordered data reconstruction • Flow control • TCP – Web Browser • UDP – Video Streaming Applications

  26. Protocol Reference Model of OSI The OSI Layers 4. Transport Layer • Connectionless and connection-oriented services • Process-Level Addressing • Multiplexing and Demultiplexing • Segmentation, Packaging and Reassembly • Connection Establishment, Management and Termination • Acknowledgments and Retransmissions • Flow Control

  27. Network layer(Layer 3) • Addressing (IPV4) • Encapsulation (Inserts a header with source and destination IPs) • Routing (Move a packet over the Internet) • Decapsulation (Open the packet and check the destination host)

  28. Protocol Reference Model of OSI The OSI Layers 3. Network Layer • Logical Addressing • Routing (where the packet is destinated to) • Datagram Encapsulation • Fragmentation and Reassembly (handling too big packets ) • Error Handling and Diagnostics ( using status messages for example )

  29. Protocol Reference Model of OSI End to end packet delivery

  30. Data link layer(Layer 2) • It is the role of the OSI Data Link layer to prepare Network layer packets for transmission and to control access to the physical media. • Allows the upper layers to access the media using techniques such as framing • Controls how data is placed onto the media and is received from the media using techniques such as media access control and error detection • Frame - The Data Link layer PDU • Node - The Layer 2 notation for network devices connected to a common medium • Media/medium - The physical means for the transfer of information between two nodes • Network - Two or more nodes connected to a common medium • The Data Link layer is responsible for the exchange of frames between nodes over the media of a physical network.

  31. Protocol Reference Model of OSI The OSI Layers 2. Data Link Layer 2.1. Logical Link Control (LLC) • Establishment and control of logical links between local devices on a network. 2.2. Media Access Control (MAC) • The procedures used by devices to control access to the network medium. • Frame sequencing • Frame acknowledgment • Addressing • Frame delimiting • Frame error checking • PDU: frame

  32. Physical layer (Layer 1) • The role of the Physical layer is to encode the binary digits that represent Data Link layer frames into signals and to transmit and receive these signals across the physical media that connect network devices. • Copper cable • Fiber • Wireless

  33. Protocol Reference Model of OSI The OSI Layers • Physical Layer • Definition of Hardware Specifications (of cables, connectors, wireless radio transceivers, network interface cards ) • Encoding and Signaling (bit representation) • Data Transmission and Reception (half duplex, full duplex ) • Topology and Physical Network Design (mesh, ring, bus) • PDU: bit

  34. Protocol Reference Model of OSI OSI Summary

  35. Conclusion • The way people learn Networking • A standard for software • A standard for hardware • Seven layers architecture • Each layer independent on the others • Similar to TCP/IP(TCP/IP explained) • OSI is used as a model for developing network aware applications(Here I mean that people use its structure to model software)

  36. 2. TCP/IP MODEL

  37. TCP/IP Model • Much older than OSI model • Consists of 4 layers instead of 7 • TCP/IP model can be mapped to the OSI model

  38. TCP/IP Model OSI & TCP/IP Models

  39. TCP/IP vs OSI

  40. TCP/IP Model TCP/IP Model Application Layer Application programs using the network Transport Layer (TCP/UDP) Management of end-to-end message transmission, error detection and error correction Network Layer (IP) Handling of datagrams : routing and congestion Data Link Layer Management of cost effective and reliable data delivery, access to physical networks Physical Layer Physical Media

  41. Comparison with TCP/IP Pretty similar to OSI TCP/IP has less layers(four) Main difference in layers is after layer 4

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