The Seven Layers of Networking - Physical to Application

Internet is everywhere. We all are using it also we started to live with Internet nowadays. I know guys You can't live without the Internet especially mobile phones.

No Facebook, No Instagram, No Whatsapp, No YouTube. Sounds ridiculous. Difficult to go back to the 90's.

Then what is the base for our Networks? Who designed the structure of Computer Networks?

In early stage of the Internet, there was lot of other networking model existed apert from OSI and TCP/IP model. For example IBM SNA, DECnet, XNS. In 1982, us military declared that TCP/IP is the default model for there communication. Also, by that time, lot of application was already there for TCP/IP model. Anyway, after this event, company started to move towards TCP/IP model.

By the year of 1989, almost all the companies adopted TCP/IP model for there computers. In year 1989 BSD Unix decided to provide TCP/IP stack. Later when Linux released, it took few year to get running any network/Internet stack in there kernel. However, it didn't took more than couple of years to adopt TCP/IP stack. This process was ended when microsoft adopted TCP/IP stack in windows 95.

Anyway, we will discuss about the OSI Model.

What is the OSI Model ?

The OSI model is an architectural model that represents networking communications.
It was introduced in 1978 by the International Organization for Standardization (ISO) to standardize the levels of services and types of interactions for computers communicating over a network.

The Open System Interconnection model is a seven-layer structure that specifies the requirements for communications between two computers.

The Seven Layers

The Physical Layer - Layer 1

The first or bottom layer of OSI model is Physical layer. It is concerned with transmitting bits over a communication channel. It is responsible for the actual physical connection between the devices.

Physical layer manages the way, how a device should connects to network media. It defines the transmission rate. It defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. 

The Physical Layer of the OSI model is only part of a LAN (Local Area Network).

The Data-Link Layer - Layer 2

This layer allows a device to access the network to send and receive messages. It is responsible for node-to-node delivery of data.

The data link layer provides access to the networking media and physical transmission across the media and this enables the data to locate its intended destination on a network. It receives the data from network layer and creates FRAMES , add physical address to these frames & pas them to physical layer.

The data link layer uses the MAC address to define a hardware address in order for multiple stations to share the same medium and still uniquely identify each other.

See How to find MAC Address of your Windows system? to know more about MAC Address.

The Network Layer - Layer 3

Network Layer is responsible for the source to destination delivery of a packet across multiple networks. It also defines logical addressing so that any endpoint can be identified.

The network layer ensures that the packet gets its point of origin to its final destination. It defines how routing works and how routes are learned so that the packets can be delivered this function is known as routing.

The networking industry has evolved to the point that it requires a common layer 3 addressing system. The Internet Protocol (IP) addresses make networks easier to both set up and connect with one another. The Internet uses IP addressing to provide connectivity to millions of networks around the world.

The Transport Layer - Layer 4

The transport layer offers end-to-end communication between end devices through a network. Depending on the application, the transport layer either offers reliable, connection-oriented or connectionless, best-effort communications. It is responsible for process-to-process delivery of the entire message.

Transport layer looks after the delivery of entire message considering all its packets and make sure that all packets are in order. It segments data from the sending host's system and reassembles the data into a data stream on the receiving host's system. At the receiver side, transport provides services to application layer and takes services form network layer.

At the source side, transport layer receives message from upper layer into packets and reassembles these packets again into message at the destination.

The boundary between the transport layer and the session layer can be thought of as the boundary between application protocols and data-flow protocols. Whereas the application, presentation, and session layers are concerned with application issues, the lower four layers are concerned with data transport issues.

The Session Layer - Layer 5

Session layer is the fifth layer of OSI Model. It has the responsibility of beginning, maintaining and ending the communication between two devices, called session. This includes the control and management of multiple bi-directional messages using dialogue control. It also provides for orderly communication between devices by regulating the flow of data.

The session layer, provides various services, including tracking the number of bytes that each end of the session has acknowledged receiving from the other end of the session. It also synchronizes dialogue between two hosts' presentation layers and manages their data exchange. It also offers provisions for efficient data transfer.

The Presentation Layer - Layer 6

The presentation layer is responsible for how an application formats the data to be sent out onto the network. The presentation layer basically allows an application to read (or understand) the message.

The presentation layer ensures that the information that the application layer of one system sends out is readable by the application layer of another system. If necessary, the presentation layer translates between multiple data formats by using a common format.

It was designed for data encryption, decryption and compression.

The Application Layer - Layer 7

The application layer is the OSI layer that is closest to the user. The application layer provides an interface for the end user operating a device connected to a network. It provides supports for services such as e-mail, file transfer, access to the world wide web.

This layer is what the user sees, in terms of loading an application (such as Web browser or e-mail) that is, this application layer is the data the user views while using these applications.

The application layer establishes the availability of intended communication partners, synchronizes and establishes agreement on procedures for error recovery and control of data integrity. It differs from the other layers in that it does not provide services to any other OSI layer, but rather only to applications outside the OSI model.

At last I am going to finish this article. Hope you all get ideas about Basic Computer Networking and What the OSI Model is.

If you have any suggestions, Kindly comment below.