Open System Interconnection Model (OSI Model)

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OSI Model

Open System Interconnection Model (OSI Model)

In this tutorial you will learn about the OSI Model (Open System Interconnection Model), Layer in the OSI Model, and types of Layers. Here you also learn about TCP/IP Model (Transmission Control Protocol/Internet Protocol), Data Transmission Modes and Data Transmission Media. Form the competitive exam perspective, the OSI Model plays a very important part of questions from this topic, Let’s start the learning.

Definition of OSI Model

The Open Systems Interconnection (OSI) Model is an intangible and logical arrangement that describes network communication between two systems by using different layer protocols. The OSI model developed by the International Standards Organization (ISO). It has seven layers to transmit data from one to another.

What is the OSI Model?

The OSI Model or the Open Systems Interconnection Model is a conceptual framework which describes the functions of a networking system. It is used for the transfer of data over a network which movers through different layers.

There are seven Layers of the OSI Model;

  1. Physical Layer
  2. Data Link Layer
  3. Network Layer
  4. Network Layer
  5. Transport Layer
  6. Session Layer
  7. Presentation Layer

OSI Model

Physical Layer

It is the lowest layer in the OSI Model. It deals with the bit-level transmission between the devise. It supports mechanical and electrical specification of the interface and transmission medium. Hub, Repeater, Modem, Caples are physical layer devices. The data unit of this layer is Bit. It converts the signal into 0s and 1s sends them to the next layer. Simplex, half-duplex and full-duplex are the transmission modes for this layer.

Product used in Physical Layer are – ATM, Ethernet and RS232

Data Link Layer

It is used for the encoding, decoding and logical organization of data bits. It makes the physical layer appear error-free. It converts the bits into frames depending on the frame size of Network Interface (NIC). Switch and Bridge is Data Link Layer devices. HDLC, ATM and LSL are the implemented protocols on this layer. It has also two sub-layer that are given below.

  • Model Access Control (MAC) – It is responsible to the physical address of the sender and receiver in the header of each frame. CSMA or CD, Ethernet are used as protocol.
  • Logical Link Control (LLC) It is responsible for frame management, error checking, and flow control of data.

Network Layer

This network provides the shortest path for transmitting data for network communication to avoid congestion. Data is transmitting in the form of packets through the logical network path. The IP address of the sender and receiver is placed in the header. Routers are used as networking devices. The IPX and TCP/IP are the implemented protocols on this layer. Routing and Logical Addressing are the functions of the layer.

Transport Layer

This layer is called as Heart of OSI Model. It is responsible for end-to-end network communication, flow control of data, error recovery and reliability and quality of data. The data in the transport layer is referred to as Segments. It is operated by the Operating System. The examples of transport layer are SPX, TCP/IP, DNS etc.

Session Layer

This layer is responsible for the establishment of the connection, maintenance of session, synchronization and ensures security. It allows adding checkpoints into the data to identify the error. This layer is the network dialog controller which allows two system into the dialog in either half-duplex and full-duplex model.

Presentation Layer

Presentation Layer performs encryption and decryption of data. It gives data in a readable format from an application layer perspective. It reduces the number of bits that need to be transmitted on the network. It offers liberty from compatibility troubles. It is called the Translation layer and Syntax layer.

Examples of this layer are; ASCII code to EBCDIC coded text file.

Application Layer

This layer focuses on process-to-process communication across an IP network and provides a firm communication interface and end-user services. It supports services such as electronic mail, remote file access, transfer, shared database management, web chat and surfing, Directory services and Network Virtual Terminal. HTTP, FTP, Telnet, SMTP and DNS have used protocols of this layer. And it is also called as Desktop Layer.

  • Session Layer, Presentation Layer and Application Layer are also known as Upper Layer or Software Layer.

What is TCP/IP Model

The TCP/IP model is a part of the Internet Protocol Suite. This model acts as a communication protocol for computer networks and connects hosts on the Internet.

TCP model is a tangible, client-server model. It is one of the most used protocols in digital network communication. It has only four layers in a data communication network.

Host-to-Network Layer – In this layer, the host has connected to the network using the protocol to send IP packets. Ethernet, Token Ring, Frame Relay are used in the Host-to-Network Layer.

Internet Layer – It transfers the internet Protocol packets to the destination. Used protocol is this layer are IP, ICMP, ARP, and IGMP.

Application Layer – Application Layer contains high-level protocols. HTTP, DNS, SMPT, FTP, NNTP, DHCP are used in application layer.

What is Data Transmission Modes?

The transmission mode is a mechanism that decides the direction of data means in which direction the data will flow. It is also referred to as data communication mode or directional mode.

Data Transmission Modes refers to the way of transferring the information or data between two connected devices

There are three types of Data Transmission Modes, and that are;

  • Simples Mode
  • Half Duplex Mode
  • Full Duplex Mode

Simples Mode – In this mode the data can be transferred in only one direction. The only one can transmit and the other can receive the data.

Example – Keyboard, Monitor, Loud Speaker, Television, etc.

Half Duplex Mode – In this mode the data can transferred in both directions, but not at the same time. Example – Walkie-talkie

Full Duplex Mode – In this mode the data can be transferred in both direction on the same transmission path. Two lines are used for sending and receiving the data. Example – Telephone network

What is Data Transmission Media?

In Data Transmission Media, data or information transferred to one place from another through the physical/wireless media which is known as Transmission Media.

Transmission media is a communication channel that carries the information for the sender to the receiver. Data is transmitted through the electromagnetic signals.

There are two types of Data Transmission Media are;

  • Guided Media/Bounded Media
  • Unguided / Unbounded Media

Guided Media

The signals are transmitted through the narrow path which made by physical links. Twisted Pair cable, Coaxal Cable and Fibre-Optic Cable are the types of Bounded Media. Twisted-pair and coaxial cable accept signals in the form of electric current. Optical fibre accepts signals in the form of light.


The signals are transmitted without using any cables. This type of transmission is known as wireless communication. Radio waves, Infrared, Micro waves are some popular types of unbound transmission media.

  • Microwave – Mobile phone, Wireless LANs, Satellite networks
  • Infrared – Short range communication (TV Remote Control, IRD Port etc.)
  • Radio Wave – Radio, Television and Paging System

So, in this tutorial you learned all about the Open System Interconnection Model (OSI Model) and its layer and types of layers, Data Transmission Mode and Media etc. you covered all the topic under OSI Media. I hope you read this tutorial thoroughly and if you have any doubt, you can ask in the comment section.

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