osi_model

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.