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Open System Interconnection(OSI) :

OSI Model was first proposed by the International Standards Organisation (ISO) to solve the multiple problems faced in telecommunication.

It is a conceptual model of telecommunication networking where the whole process id divided into seven effective layers. It synchronizes the whole process and helps one understand the interoperation of the driver’s communication system under the standard protocol. The 7 layers we are talking about are abstraction layers and each layer is connected to either one or two layers depending on its position. The interlinked layers serve one another to forward the communication process.

Seven Layers of the OSI Model:-

  1. Physical Layer
  2. Data Link layer
  3. Network Layer
  4. Transport Layer
  5. Session Layer
  6. Presentation Layer
  7. Application Layer

Physical Layer –

OSI Model, Layer 1 conveys the bitstream – electrical impulse, light or radio signal through the network at the electrical level. It provides the hardware means of sending and receiving data, including defining cables, cards, and physical aspects. It basically shows the physical topology of a network.

Data Link Layer –

At OSI Model, Layer 2, data packets are encoded and decoded into bits. The data link layer is divided into two sub-layers:

  • The Media Access Control (MAC) layer: The MAC sublayer is responsible for the framing of data and It includes source and destination’s physical address(MAC) into the header.
  • The Logical Link Control (LLC) layer: The LLC layer controls frame sequencing and error checking.

Network Layer –

Layer 3 provides routing technologies, routing and forwarding are functions of this layer, as well as addressing. It includes the IP address of the source and destination’s devices into the header and converts the data into the packet.

Transport Layer –

The transport layer is one of the most important layers in the OSI Model, it is responsible for the following functions:

  1. End-to-end delivery of data.
  2. Selection of method of transfer (Connection-Oriented/Connection Less)
  3. Segmentation of data
  4. Flow control (Windowing)
  5. Error correction

Session Layer –

This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations between applications at each end. Time and clock synchronization and scheduling occur here and it also decides the mode of transmission.

Presentation Layer –

This layer is responsible for encapsulation of data & various other tasks :-

  1. Code formatting(.txt, .jpeg, .mp3, etc.)
  2. Encryption/Decryption of data.
  3. Compression/Decompression.

Application Layer –

OSI Model, Layer 7, supports application and end-user processes. Communication partners are identified and quality of service is identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level.