What is the OSI Model?
What is the OSI Model?
The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes how computer networks communicate. It divides network communication into seven layers, each with a specific function, ensuring smooth data transmission across different systems and technologies.
OSI Model – 7 Layers
| Layer | Name | Function | Protocols/Examples |
|---|---|---|---|
| 7 | Application | End-user interaction, network services | HTTP, FTP, SMTP, DNS |
| 6 | Presentation | Data encryption, compression, translation | SSL, TLS, JPEG, ASCII |
| 5 | Session | Manages sessions between applications | PPTP, NetBIOS, RPC |
| 4 | Transport | End-to-end communication, reliability | TCP, UDP |
| 3 | Network | Routing, addressing | IP, ICMP, ARP |
| 2 | Data Link | MAC addressing, error detection | Ethernet, PPP, MAC |
| 1 | Physical | Transmission of raw data | Cables, Wi-Fi, Fiber optics |
Detailed Breakdown of Each Layer
1. Physical Layer
1. Deals with raw bit transmission over physical media.
2. Includes cables (Ethernet, fiber optics), Wi-Fi, and connectors.
3. Converts digital data into electrical, optical, or radio signals.
2. Data Link Layer
1. Ensures error-free data transfer between two directly connected nodes.
2. Uses MAC (Media Access Control) addresses for device identification.
3. Devices: Switches, Network Interface Cards (NICs).
4. Protocols: Ethernet, PPP (Point-to-Point Protocol).
3. Network Layer
1. Handles routing of data between different networks.
2. Uses IP (Internet Protocol) addresses to identify devices.
3. Devices: Routers.
4. Protocols: IPv4, IPv6, ICMP (Ping), ARP.
4. Transport Layer
1. Manages end-to-end communication and data delivery.
2. Uses TCP (reliable, connection-oriented) and UDP (faster, connectionless).
3. Ensures error detection and data segmentation.
5. Session Layer
1. Manages and controls sessions (connections) between applications.
2. Example: Logging into a remote server or handling multiple web sessions.
3. Protocols: NetBIOS, RPC (Remote Procedure Call), PPTP.
6. Presentation Layer
1. Formats, encrypts, and compresses data for transmission.
2. Ensures that data sent by one system is readable by another.
3. Protocols: SSL/TLS (for encryption), JPEG, ASCII, Unicode.
7. Application Layer
1. The user-facing layer where applications interact with the network.
2. Examples: Web browsing, email, file transfers.
3. Protocols: HTTP/HTTPS, FTP, SMTP, DNS, Telnet.
Why is the OSI Model Important?
✅ Standardization – Ensures compatibility between different networking devices and systems.
✅ Troubleshooting – Helps network engineers diagnose network issues by isolating problems at specific layers.
✅ Scalability – Makes it easier to upgrade or modify individual layers without affecting the whole system.
