What is OSI Reference Model
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The OSI (Open Systems Interconnection) Reference Model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven abstraction layers. Developed by the International Organization for Standardization (ISO), it provides a systematic approach to understanding and designing computer networks. Let's dive deeper into each layer:
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1. Physical Layer:
The foundation of the OSI model, responsible for transmitting raw data bits over a physical medium such as cables or wireless signals.
Defines characteristics like voltage levels, data rates, and connector types.
Examples include Ethernet cables, fiber optic cables, and wireless signals.
2. Data Link Layer:
Manages the physical transmission of data and provides error detection and correction.
Divided into two sublayers: Logical Link Control (LLC) and Media Access Control (MAC).
LLC ensures error-free transmission between devices, while MAC controls access to the physical medium.
Examples include Ethernet switches, bridges, and protocols like Point-to-Point Protocol (PPP).
3. Network Layer:
Handles routing and forwarding of data packets between different networks.
Determines the best path for data transmission based on network conditions and congestion.
Examples include IP (Internet Protocol), routing protocols like OSPF and BGP, and devices like routers.
4. Transport Layer:
Ensures reliable and orderly delivery of data between devices.
Divided into two main protocols: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).
TCP provides connection-oriented, reliable data transfer with flow control and error correction.
UDP is connectionless and used for applications where speed is more critical than reliability.
Examples include TCP for web browsing, email, and file transfer, and UDP for real-time streaming and online gaming.
5. Session Layer:
Manages communication sessions between applications running on different devices.
Establishes, maintains, and synchronizes the interactions, including session setup, data exchange, and teardown.
Examples include NetBIOS for Windows file sharing and RPC (Remote Procedure Call) for client-server communication.
6. Presentation Layer:
Responsible for data formatting, encryption, and compression.
Translates data from the application layer into a format suitable for transmission over the network.
Handles data encryption to ensure secure communication.
Examples include encryption protocols like SSL/TLS and file formats like JPEG, GIF, and MPEG.
7. Application Layer:
The topmost layer, interacts directly with end-users and application software.
Provides network services such as email (SMTP), web browsing (HTTP), file transfer (FTP), and remote login (SSH).
Examples include web browsers, email clients, and file transfer utilities.
Understanding the OSI model helps network engineers and developers design, implement, and troubleshoot network architectures more effectively by providing a clear framework for communication protocols and interactions between different network components.