Layers Of OSI Model In Networking

Here i am going to explain about OSI layers.

Make sure you understand the seven layers of the OSI model and how communications take place at the different layers.

Firstly, The Open Systems Interconnection (OSI) model was created by the International Organization for Standardization (ISO) to describe how computer networks are structured and how data signals travel from one system to another. The model divides the network into seven layers, with physical hardware at the bottom and software applications at the top.

1) Physical Layer (Layer 1):

Physical layer is the lower layer from OSI, 

It is responsible for the actual physical connection between the devices. The physical layer contains information in the form of Bits. It is responsible for transmitting individual bits from one node to the next.

* Hub, Repeater, Modem, Cables are Physical Layer devices. 

2) Data Link Layer (DLL) (Layer 2) :

The data link layer is responsible for the node to node delivery of the message. The data-link layer contains information in the form of Frames. The main function of this layer is to make sure data transfer is error-free from one node to another, over the physical layer.

Data Link Layer is divided into two sub layers :  

Logical Link Control (LLC)

Media Access Control (MAC)

The functions of the data Link layer are :  Framing, Physical addressing, Error Control, Flow Control and Access Control

* Switch & Bridge are Data Link Layer devices. 

3) Network Layer (Layer 3) :

Network layer works for the transmission of data from one host to the other located in different networks. The Network layer contains information in the form of Packets. It also takes care of packet routing i.e. selection of the shortest path to transmit the packetnetworklayer is known as routing.

Logical Addressing: In order to identify each device on internetwork uniquely, network layer defines an addressing scheme.

 *Router is the Network  Layer devices. 

4)Transport Layer (Layer 4) :

It is responsible for the End to End Delivery of the complete message. The transport layer also provides the acknowledgement of the successful data transmission and re-transmits the data if an error is found. The Transport layer contains information in the form of Segments.

The services provided by the transport layer :

Connection Oriented Service: It is a three-phase process which include 

– Connection Establishment 

– Data Transfer 

– Termination / disconnection 

In this type of transmission, the receiving device sends an acknowledgement, back to the source after a packet or group of packet is received. This type of transmission is reliable and secure.

Connection less service: It is a one-phase process and includes Data Transfer. In this type of transmission, the receiver does not acknowledge receipt of a packet. 

This approach allows for much faster communication between devices. Connection-oriented service is more reliable than connectionless Service.

*Transport Layer is called as Heart of OSI model. 

5) Session Layer (Layer 5) :

This layer is responsible for establishment of connection, maintenance of sessions, authentication and also ensures security. 

The functions of the session layer are: Session establishment, maintenance and termination

6) Presentation Layer (Layer 6) :

Presentation layer is also called the Translation layer. The data from the application layer is extracted here and manipulated as per the required format to transmit over the network. 

The functions of the presentation layer are : Translation, Encryption/ Decryption, Compression

7) Application Layer (Layer 7) :

Application layer which is implemented by the network applications. These applications produce the data, which has to be transferred over the network

Ex: Application – Browsers, Skype Messenger etc. 

*Application Layer is also called as Desktop Layer.