OSI model

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.