Home » » OSI model

OSI model

10:52 PM    

What is OSI model?

The OSI model (Open System Interconnection) model defines a computer networking framework to implement protocols in seven layers. A protocol in the networking terms is a kind of negotiation and rule in between two networking entities.

Layers of OSI model:

Physical layer

The Physical layer is also called as the Layer 1. Here are the basic functionalities of the Physical layer:
  • Responsible for electrical signals, light signal, radio signals etc.
  • Hardware layer of the OSI layer
  • Devices like repeater, hub, cables, ethernet work on this layer
  • Protocols like RS232, ATM, FDDI, Ethernet work on this layer

Data Link layer

The data link layer is also called as the Layer 2 of the OSI model. Here are the basic functionalities of the data link layer:
  • Responsible for encoding and decoding of the electrical signals into bits.
  • Manages data errors from the physical layer
  • Convers electrical signals into frames
  • The data link layer is divided into two sub-layers
    • The Media Access Control (MAC) layer
    • Logical Link Control (LLC) layer.
  • The MAC sublayer controls how a computer on the network gains access to the data and permission to transmit it.
  • The LLC layer controls frame synchronization, flow control and error checking.
  • MAC address is a part of the layer 2.
  • Devices like Switch work at this layer

Network Layer

The Network layer is also called as the layer 3 of the OSI model. Here are the basic functionalities of the network layer:
  • Switching and routing technologies work here
  • Creates logical paths between two hosts across the world wide web called as virtual circuits
  • Routes the data packet to destination
  • Routing and forwarding of the data packets.
  • Internetworking, error handling, congestion control and packet sequencing work at this layer
  • Router works at layer three
  • Different network protocols like TCP/ IP, IPX, AppleTalk work at this layer

Transport layer

The Transport  layer is also called as the layer 4 of the OSI model. Here are the basic functionalities of the Transport layer:
  • Responsible for the transparent transfer of data between end systems
  • Responsible for end-to-end error recovery and flow control
  • Responsible for complete data transfer.
  • Protocols like SPX, TCP, UDP work here

Session layer

The Session  layer is also called as the layer 5 of the OSI model. Here are the basic functionalities of the Session layer:
  • Responsible for establishment, management and termination of connections between applications.
  • The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end.
  • It deals with session and connection coordination.
  • Protocols like NFS, NetBios names, RPC, SQL work at this layer.

Presentation layer:

The Presentation layer is also called as the layer 6 of the OSI model. Here are the basic functionalities of the presentation layer:
  • Responsible for data representation on your screen
  • Encryption and decryption of the data
  • Data semantics and syntax
  • Layer 6 Presentation examples include encryption, ASCII, EBCDIC, TIFF, GIF, PICT, JPEG, MPEG, MIDI.

Application Layer:

The Application layer is also called as the layer 7 of the OSI model. Here are the basic functionalities of the Application layer:
  • Application layer supports application, apps, and end-user processes.
  • Quality of service
  • This layer is responsible for application services for file transfers, e-mail, and other network software services.
  • Protocols like Telnet, FTP, HTTP work on this layer.