ISO and the OSI Model

 

ISO and the OSI Model

ISO

The International Organization for Standardization (ISO) was established in 1947 as an international body responsible for developing worldwide standards in different fields, including computer networking.

ISO introduced the:

Open Systems Interconnection (OSI) Model

in the late 1970s.

What is the OSI Model?

The OSI Model is a layered framework used to understand, design, and standardize network communication.

It is:

  • Not a protocol
  • A conceptual model

The OSI model allows:

  • Communication between different computer systems
  • Interoperability between hardware and software from different vendors

Layers of the OSI Model

The OSI model consists of:

7 layers

Each layer performs specific networking functions.


OSI Layers and Their Functions

LayerFunction
7. Application    Provides network services to users and applications
6. Presentation    Data translation, encryption, and compression
5. Session    Establishes, manages, and terminates sessions
4. Transport    End-to-end delivery, reliability, flow and error control
3. Network    Logical addressing and routing
2. Data Link    Framing, physical addressing, error detection
1. Physical    Transmission of bits over the medium

Brief Explanation of Each Layer

7. Application Layer

Function

Provides services directly to user applications.

Examples

  • Web browsing
  • E-mail
  • File transfer

Protocols

  • HTTP
  • FTP
  • SMTP
  • DNS

6. Presentation Layer

Function

Responsible for:

  • Data formatting
  • Encryption/decryption
  • Compression

It ensures that data sent by one system can be understood by another.

5. Session Layer

Function

  • Establishes communication sessions
  • Maintains dialogs
  • Terminates sessions after communication

It controls synchronization between devices.

4. Transport Layer

Function

Provides:

  • End-to-end communication
  • Flow control
  • Error control
  • Segmentation and reassembly

Protocols

  • TCP
  • UDP

3. Network Layer

Function

Responsible for:

  • Logical addressing
  • Routing
  • Path selection

Protocol

  • IP

Device

  • Router

2. Data-Link Layer

Function

  • Framing
  • Physical (MAC) addressing
  • Error detection
  • Node-to-node delivery

Device

  • Switch

1. Physical Layer

Function

Responsible for:

  • Transmission of bits
  • Electrical, optical, or wireless signaling

Examples

  • Cables
  • Connectors
  • Radio signals

Why OSI Model Was Not Widely Adopted

Although the OSI model was important conceptually, TCP/IP became dominant because:

  1. TCP/IP was already widely used.
  2. Some OSI layers were not fully defined.
  3. OSI implementation performance was not as efficient as TCP/IP.

Importance of the OSI Model

The OSI model helps:

  • Understand network communication
  • Design networking systems
  • Troubleshoot network problems
  • Standardize networking concepts

Summary

The OSI model, developed by ISO, is a seven-layer reference model used for understanding and designing computer network communication. Each layer performs specific functions, ranging from user applications at the application layer to bit transmission at the physical layer. Although TCP/IP became the practical standard for the Internet, the OSI model remains an important educational and conceptual framework in networking.

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