COMPUTER NETWORK NOTES , IOE, BSCCSIT, BCA 

OSI REFERENCE MODEL 

The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven abstraction layers. It was developed by the International Organization for Standardization (ISO) to promote interoperability and facilitate understanding and design of network architectures. Each layer in the OSI model has a specific function, and communication between layers is achieved through well-defined interfaces. Here are the seven layers of the OSI model:

• Physical Layer (Layer 1):
  • Function: The physical layer deals with the physical connection between devices. It specifies the characteristics of the hardware, such as cables, connectors, and signaling methods, needed to transmit raw bits over a physical medium.
• Data Link Layer (Layer 2):
  • Function: The data link layer provides error detection and correction, as well as the framing of data into frames for reliable transmission over the physical layer. It also manages access to the physical medium through protocols like Ethernet.
• Network Layer (Layer 3):
  • Function: The network layer is responsible for logical addressing, routing, and forwarding of data packets between devices on different networks. IP (Internet Protocol) operates at this layer.
• Transport Layer (Layer 4):
  • Function: The transport layer ensures end-to-end communication and data flow control. It manages segmentation, reassembly, error recovery, and flow control. Examples of transport layer protocols include TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).
• Session Layer (Layer 5):
  • Function: The session layer establishes, manages, and terminates sessions (dialogues) between applications. It handles the synchronization and coordination of data exchange between systems.
• Presentation Layer (Layer 6):
  • Function: The presentation layer is responsible for data translation, encryption, and compression. It ensures that data is presented in a readable format for the application layer. It also handles character encoding, data compression, and encryption/decryption.
• Application Layer (Layer 7):
  • Function: The application layer provides network services directly to end-users or applications. It allows software applications to communicate over a network. Protocols such as HTTP (Hypertext Transfer Protocol), FTP (File Transfer Protocol), and SMTP (Simple Mail Transfer Protocol) operate at this layer.

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