OSI Model Overview

OSI Model Overview

The OSI (Open Systems Interconnection) model is a 7-layered framework for designing and implementing computer networks.

Layers of the OSI Model

1. Physical Layer (Layer 1)
   • Defines the physical means of data transmission (e.g., cables, Wi-Fi)
   • Specifies voltage levels, data rates, and network topology
2. Data Link Layer (Layer 2)
   • Provides error-free transfer of data frames between nodes on the same network
   • Manages access to the network, resolves collisions, and corrects errors
3. Network Layer (Layer 3)
   • Routes data between networks
   • Provides logical addressing, routing, and congestion control
4. Transport Layer (Layer 4)
   • Ensures reliable data transfer between devices
   • Provides error detection and correction, as well as flow control
5. Session Layer (Layer 5)
   • Establishes, manages, and terminates connections between applications
   • Controls dialogue between applications and manages data exchange
6. Presentation Layer (Layer 6)
   • Converts data into a format that can be understood by the receiving device
   • Manages data encryption, compression, and formatting
7. Application Layer (Layer 7)
   • Provides services to end-user applications (e.g., email, file transfer, web browsing)
   • Supports functions such as email, FTP, and HTTP

Key Concepts

• Each layer communicates with its peer layer on other devices through a standardized interface
• Data is encapsulated with headers and trailers as it moves down the stack, and de-encapsulated as it moves up
• The OSI model is a theoretical framework, and not all protocols follow it strictly (e.g., TCP/IP)

OSI Model Overview

• The OSI model is a 7-layered framework for designing and implementing computer networks

Layers of the OSI Model

• Physical Layer (Layer 1)
  • Defines physical means of data transmission (e.g., cables, Wi-Fi)
  • Specifies voltage levels, data rates, and network topology
• Data Link Layer (Layer 2)
  • Provides error-free transfer of data frames between nodes on the same network
  • Manages access to the network, resolves collisions, and corrects errors
• Network Layer (Layer 3)
  • Routes data between networks
  • Provides logical addressing, routing, and congestion control
• Transport Layer (Layer 4)
  • Ensures reliable data transfer between devices
  • Provides error detection and correction, as well as flow control
• Session Layer (Layer 5)
  • Establishes, manages, and terminates connections between applications
  • Controls dialogue between applications and manages data exchange
• Presentation Layer (Layer 6)
  • Converts data into a format that can be understood by the receiving device
  • Manages data encryption, compression, and formatting
• Application Layer (Layer 7)
  • Provides services to end-user applications (e.g., email, file transfer, web browsing)
  • Supports functions such as email, FTP, and HTTP

Key Concepts

• Each layer communicates with its peer layer on other devices through a standardized interface
• Data is encapsulated with headers and trailers as it moves down the stack, and de-encapsulated as it moves up
• The OSI model is a theoretical framework, and not all protocols follow it strictly (e.g., TCP/IP)

OSI Model

Physical Layer (Layer 1)

• Defines the physical means of transmitting data between devices, including cable specifications and wireless transmission
• Concerned with the physical transmission of raw bits over a physical medium
• Responsible for bit-level transmission and reception, signal encoding and decoding, and data transmission and reception

Data Link Layer (Layer 2)

• Provides error-free transfer of data frames between nodes on the same network
• Ensures error detection and correction through framing, error detection, and correction
• Manages access to the network and resolves collisions through medium access control (MAC)
• Functions include framing, error detection, flow control, and MAC

Network Layer (Layer 3)

• Routes data between nodes on different networks
• Provides logical addressing and routing through IP addressing
• Concerned with the routing of data between networks, including congestion control
• Functions include routing, logical addressing, and congestion control

Transport Layer (Layer 4)

• Provides reliable data transfer between devices
• Ensures error-free and sequential delivery of data through segmentation and reassembly
• Concerned with the transportation of data between devices, including connection establishment and termination
• Functions include segmentation, reassembly, connection establishment, and error detection and correction

Session Layer (Layer 5)

• Establishes, manages, and terminates connections between applications
• Controls the dialogue between applications through session establishment and termination
• Concerned with the synchronization and management of dialogues, including synchronization and dialogue management