osi model cheat sheet

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25-11-2024

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The OSI Model (Open Systems Interconnection Model) is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers. This cheat sheet provides a concise overview of each layer, its primary functions, and examples of associated protocols and technologies.

1. Physical Layer (Layer 1)

Overview:

The physical layer is responsible for the physical connection between devices. It deals with the transmission and reception of raw bitstreams over a physical medium.

Key Functions:

• Defines hardware specifications such as cables, switches, and wiring.
• Establishes the electrical and physical specifications for devices.
• Manages data rate, synchronization, and physical topologies.

Examples:

• Ethernet (IEEE 802.3)
• USB (Universal Serial Bus)
• Fiber optics

2. Data Link Layer (Layer 2)

Overview:

The data link layer provides node-to-node data transfer and handles error correction from the physical layer. It ensures reliable data transfer across the physical network.

Key Functions:

• Framing: Encapsulates packets into frames.
• Addressing: Uses MAC addresses for identification on the network.
• Error detection and correction.

Examples:

• Ethernet (IEEE 802.3)
• Wi-Fi (IEEE 802.11)
• Point-to-Point Protocol (PPP)

3. Network Layer (Layer 3)

Overview:

The network layer manages the delivery of packets across multiple networks. Its primary function is routing and forwarding.

Key Functions:

• Logical addressing (IP addresses).
• Routing decisions based on network conditions.
• Fragmentation and reassembly of packets.

Examples:

• Internet Protocol (IP)
• Internet Control Message Protocol (ICMP)
• Routing Information Protocol (RIP)

4. Transport Layer (Layer 4)

Overview:

The transport layer ensures complete data transfer and manages error recovery and flow control.

Key Functions:

• Segmentation of data into smaller packets.
• End-to-end communication through ports.
• Reliable delivery (connection-oriented) and unordered delivery (connectionless).

Examples:

• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)

5. Session Layer (Layer 5)

Overview:

The session layer manages sessions between applications. It establishes, maintains, and terminates connections.

Key Functions:

• Session establishment and management.
• Synchronization of data exchange.
• Dialog control (half-duplex or full-duplex).

Examples:

• NetBIOS
• RPC (Remote Procedure Call)

6. Presentation Layer (Layer 6)

Overview:

The presentation layer translates data for the application layer. It formats and encrypts data for the application layer if necessary.

Key Functions:

• Data translation and encoding (e.g., ASCII, EBCDIC).
• Data compression.
• Encryption and decryption for security.

Examples:

• JPEG (image format)
• SSL/TLS (secure communication protocol)

7. Application Layer (Layer 7)

Overview:

The application layer is the closest layer to the end-user. It provides network services directly to applications.

Key Functions:

• Interface between user applications and the network.
• Provides protocols for file transfers, email, and web browsing.
• Facilitates data exchange and network service requests.

Examples:

• HTTP/HTTPS (Hypertext Transfer Protocol)
• FTP/SFTP (File Transfer Protocol)
• SMTP (Simple Mail Transfer Protocol)

Summary

The OSI Model serves as a fundamental guide for understanding and troubleshooting network communication. Each layer has specific functions and protocols that ensure efficient data transmission and communication across networks. Use this cheat sheet as a quick reference to grasp the basic structure and components of the OSI Model.

By familiarizing yourself with the OSI Model, you'll enhance your networking knowledge, making it easier to visualize and comprehend complex networking concepts. Whether you're a student, IT professional, or simply a tech enthusiast, this cheat sheet will serve as a valuable resource in your studies and practices.