Full form of OSI model: OSI stands for Open System Interconnection.

OSI Model: The OSI model was developed by international organization for standrization (ISO) and introduce in 1984. This is layered architecture consist of 7 layers. Each layer defines a set of functions takes in data connection.

OSI model is a reference model which shows how application communication in the network.

In the starting Each vendor had its own proprietary solution. The bad part was that one vendor’s solution was not compatible with another vendor’s solution. This is where the idea for the OSI model was born, having a layered approach to networks our hardware vendors would design hardwarefor the network, and others could develop software for the application layer. Using an open model which everyone agrees on means we can build networks that are compatible with each other.

To fix this problem the International Organisation for standrization (ISO) researched different network models and the result is the OSI-model which was released in 1984. Nowadays most vendors build networks based on the OSI model and hardware from different vendors compatible.

OSI model is best way to learn about the network.







                            

                                                 7 Layers of OSI Model:

7. Application Layer: 

Application layer is responsible for providing an interface for the user to interact with application and services. In other words application layer is creating a data files and an emails. Protocol data unit (PDU) of the application layer is "DATA".

Application layer protocols: Telnet (23), SSH(22), FTP(21), TFTP(69), HTTP(80), HTTPS(443), NTP(123), DNS(53) etc.

6. Presentation Layer:

Presentation layer is responsible for defining the standard formats to the data presentation. This layer shows the format of the data like mp4, AVI, jpg,png etc. This layer make sure that information is readable for the application layer by formatting and structuring the data. The PDU of this layer is DATA.

The major function describe at this layer is 

a. Sending - Receiving

b. Encoding - Decoding

c. Encription - Decription

d. Compression- Decompression

5. Session Layer: 

Session layer is responsible for establishing, maintaining and terminating the session between the two host. when you are browsing a website on the internet you are probably not the only user of the webserver hosting that website. This webserver needs to keep track of all the different "sessions". For the every session there are different session and port number. The PDU of the session layer is DATA.

4. Transport Layer: 

Transport layer describe the end to end data delivering mechanism between application in the network. Data transmission, segment and flowcontrol  and error correction at this layer.

TCP and UDP works on transport layer. The PDU of the transport layer is segmention of the data. Segmentation of the data means small chunks of the data. Add the source port and destination port.

TCP: Stands for transmission control protocol which send data in reliable way.

UDP: Stands for user datagram protoclo which sends data in unreliable way.

3. Network Layer:

Network layer provide logical address and path determination (Routing). At this layer adds the packet, IP address and routing. The PDU of this layer is packet. Wrap up of the data source ip and destination ip at this layer.

2. Data link Layeral 

This is responsible for the framing of the data. Adds the frame on the data. Adds the source mac address and destination mac address on the data. PDU is framing. It has two sub layer

a. MAC (Media access control): It provides reliable transit of data across a physical link.

b. LLC (Logical Link control): It provides communication with network layer.

The major functions of data link layer are

  • Framming
  • Physical addressing
  • Flow control
  • Error control
  • Access control

1. Physical Layer:

This layer defines the electrical, mechanical and function specific for communication between the network devices. In other word we can say, It is the  process to converts binary data into signals.