OSI model Open System Interconnection by ISO. Basic reference model: ISO-7498, The OSI model provides a defined way of Data Transfer over a network. It enables the troubleshooting of incompatibility issues among various networking systems that are privately operated and owned. It is also used to enable communication between different systems without requiring any changes to the hardware or software.


  • Purpose of OSI model
  • Need for OSI Model
  • Why it is Used
  • 7 OSI Layers
  • Interaction between the OSI layer
  • OSI Reference Model
  • Data Encapsulation in TCP/IP
  • Advantages & Disadvantages of OSI Model

Need of OSI 

  • To find hidden Physical Connections.
  • For Proper Handshaking.
  • Negotiate various Connection Properties.
  • Begin and end a message correctly.
  • Examine corrupted or incorrectly formatted messages.
  • Close the Session and/or Connection.

ISO-Organization for standardization

ISO (International Organization for Standardization) defines products and services that are safer, more reliable, and of high quality.

The organization, which was founded on February 23, 1947, develops and publishes worldwide proprietary, industrial, and commercial standards. The company’s headquarters are in Geneva, Switzerland.

Why International Standards are used?

  • To improve operations, increase customer satisfaction, and gain access to new markets, international standards are used.
  • Improve Productivity and Competitiveness.
  • Access New Markets.
  • Reduce the negative environmental impact.
  • Move Services and Technologies from Country to Country Provide .
  • Consumers with Safe, Reliable, and High-Quality Confidence.

Layered Network Model

  • Communication is broken down into smaller, simpler parts.
  • Facilitates the communication process.
  • Allows changes to be made in one layer without affecting the operation of other layers.
  • Create a Standard for Different Manufacturers.
  • Allows different hardware and software to interact with one another.
  • Complexity is reduced.

7 Layers of OSI Model

1. Physical Layer

In the OSI Model, the Physical layer is the first (lowest) layer. Its also known as PHY. This layer encompasses the operation of hardware that sends and receives data over a medium. This layer’s hardware includes repeaters, hubs, and so on.

2. Data-Link Layer

Layer 2 in the OSI model is the Data-Link layer. This layer handles data error checking and media access control. It is made up of two sub-layers. SNAP and Ethernet II are examples of this layer’s logical link control (LLC) and media access control (MAC).

3. Network Layer

In the OSI model, the network layer is layer 3. It is in charge of packet routing across the network. Using Routing Protocol, the network layer selects the best path for a packet to transmit to the network. For instance, IP (Internet Protocol), IPX (Internet Protocol Exchange), and so on.

4. Transport Layer

In the OSI Model, the transport layer is layer 4. This layer ensures that messages arrive on time. Before sending a message, it divides the message into smaller packets and aligns them in sequence. TCP (Transport Control Protocol), SPX, and other protocols that operate at this level are examples (Sequence Packet Exchange).

5. Session Layer

In the OSI Model, the session layer is layer 5. This layer creates a link between the applications running on both ends. It establishes and terminates sessions between applications. Software Ports and RPC Portmapper are two examples of this layer.

6. Presentation Layer

In the OSI Model, the presentation layer is layer 6. This layer serves as the Application Layer’s Data Translator. This layer codes before sending and decodes after receiving functions that apply to the application layer. FTP (File Transfer Protocol), DNS (Domain Name Server), and other protocols that operate at this level are examples.

7. Application Layer

In the OSI Model, the application layer is layer 7. It ensures the accuracy of data sent from one computer to another. This layer communicates with the software applications. Application Layer Web Browser, E-mail, and Other Examples.

Interaction Between the OSI layers

OSI Reference Model

Protocols of OSI Model

  • POP3:- (Post Office Protocol)POP3 enables users to download email from the internet.
  • SMTP:- (Simple Mail Transfer Protocol)When sending email from one email server to another, we use SMTP.
  • Usenet:- Usenet is a network that generates, stores, and retrieves articles/posts from internet users.
  • HTTP:-(Hypertext Transfer Protocol)An application layer protocol is HTTP.
    Its purpose is to allow communication between the user and the server
  • FTP:-(File Transfer Protocol)It’s a network protocol that allows you to send files from one computer to another over the internet.
  • Telnet:- Telnet is a network protocol for controlling and communicating with other servers on the network over the Internet or a local area network.
  • DNS:- (Domain Name System)DNS an internet-connected service’s systematic distributed naming system.
  • SNMP:-(Simple Network Management Protocol)SNMP is a Standard Protocol for Device Management on IP Networks.
  • NFS:-(Network File System)NFS allows a user to Access Files over the network.

Advantages of OSI Model

  • Reduces Complexity.
  • Standardize Interfaces.
  • Facilitates Flexible Engineering.
  • Provides Interoperability between Merchants.
  • Guarantees to provide Interoperable Technology.
  • Accelerates Evolution of Network Technology.
  • Simplifies Teaching and Learning of networking.

Disadvantages of OSI Model

  • Because the OSI requires an agreement between users and service providers to establish a connection for mode transfer, it is slow.
  • It does not refer to any particular implementation, such as the TCP/IP model.
  • Network Layers often Splits into Sub-layers.
  • The OSI Model is inapplicable to telecommunication applications because these applications require some choices that differ in how hardware/software communicates.

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