OSI MODEL

OSI MODEL

The OSI Model is a conceptual framework that defines how data is transmitted between devices on a network.

Contents

This cheatsheet provides information about each layer of the OSI Model, including:

• number of layer;
• name;
• function;
• type of data processed;
• common protocols and standards.

OSI-Model Cheatsheet

Layer 1: Physical

• Function: Transmits raw bit streams over a physical medium.
• Components: Cables, fibers, physical network interfaces, hubs, repeaters.
• Role: Defines physical and electrical specifications of devices and media.

Layer 2: Data Link

• Function: Manages node-to-node data transfer and error handling.
• Sublayers: Media Access Control (MAC), Logical Link Control (LLC).
• Components: Switches, bridges, network interface cards (NICs).
• Protocols: Ethernet, PPP, Switching, ARP.

Layer 3: Network

• Function: Manages device addressing, tracks the location of devices, and determines the best way to move data.
• Components: Routers, layer 3 switches.
• Protocols: IP, ICMP, IPSec, IGMP, OSPF, BGP.

Layer 4: Transport

• Function: Provides reliable data transfer across a network.
• Characteristics: TCP (connection-oriented) and UDP (connectionless).
• Role: Manages end-to-end message delivery, error recovery, and flow control.

Layer 5: Session

• Function: Manages sessions or connections between applications.
• Role: Establishes, manages, and terminates connections between applications.
• Protocols: NetBIOS, SMB, RPC, PPTP.

Layer 6: Presentation

• Function: Translates data between the application layer and the network.
• Role: Data encryption, decryption, compression, and translation.
• Examples: SSL, TLS, MIME, ASCII, EBCDIC, JPEG, MPEG.

Layer 7: Application

• Function: Closest to the end user. Interacts with software applications that implement a communicating component.
• Role: HTTP, FTP, SMTP, DNS, Telnet, SNMP, and more.
• Characteristics: Serves as the window for users and application processes to access network services.

Understanding the OSI Model

• Data Encapsulation: Each layer adds its own header (or trailer) to the data as it passes through.
• Data Flow: Data flows down the layers on the sending end and up the layers on the receiving end.
• Layer Interaction: Each layer on the sending device communicates with its corresponding layer on the receiving device.

Practical Applications

• Troubleshooting: Helps in isolating network issues by layer.
• Network Design: Guides the design and understanding of network architectures.
• Protocol Implementation: Assists in understanding and implementing network protocols.

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