The OSI Reference Model (Open Systems Interconnection Model) is a conceptual framework used to understand and describe how different networking protocols and systems communicate with each other.
It breaks down the complex process of data communication into 7 distinct layers, each with specific functions.
🔹 7 Layers of the OSI Model (Top to Bottom)
7. Application Layer
- What it does: Provides services directly to the user and applications.
- Examples: Web browsers, email clients, file transfer, remote login.
- Protocols: HTTP, HTTPS, FTP, SMTP, POP3, DNS.
6. Presentation Layer
- What it does: Ensures data is in a readable format for the application layer. Handles encryption, compression, translation.
- Examples: Data formatting, SSL/TLS encryption, JPEG, GIF, MP3.
5. Session Layer
- What it does: Establishes, manages, and terminates sessions (connections) between applications.
- Examples: Remote Procedure Calls (RPC), NetBIOS, managing login sessions.
4. Transport Layer
- What it does: Provides reliable or unreliable delivery of data between devices. Ensures proper sequencing and error checking.
- Protocols:
- TCP (Transmission Control Protocol – reliable, connection-oriented)
- UDP (User Datagram Protocol – faster, connectionless)
3. Network Layer
- What it does: Handles logical addressing, routing, and path determination.
- Examples: Routers operate here.
- Protocols: IP (IPv4, IPv6), ICMP, OSPF, RIP, BGP.
2. Data Link Layer
- What it does: Provides node-to-node communication, error detection, and framing. Uses MAC addresses.
- Examples: Switches, Ethernet, PPP, ARP.
- Sub-layers:
- LLC (Logical Link Control)
- MAC (Media Access Control)
1. Physical Layer
- What it does: Deals with raw bits transmission over physical media (cables, wireless signals). Defines hardware specs.
- Examples: Hubs, repeaters, cables, fiber optics, Wi-Fi signals.
🔹 Easy Way to Remember (Mnemonic)
All People Seem To Need Data Processing
(Application, Presentation, Session, Transport, Network, Data Link, Physical)
✅ In summary:
- Upper layers (7–5): Application-related
- Middle (4): End-to-end communication (Transport)
- Lower layers (3–1): Data delivery through network
The Lazy Networker 
Leave a comment