OSI Model – The 7 Layers of Networking
The Open Systems Interconnection (OSI) model is a conceptual framework used to understand network interactions in seven distinct layers. Each layer serves specific functions and communicates with the layers directly above and below it.
Layer Details
7 – Application Layer
✚
Provides network services to end‑user applications (e.g., HTTP, FTP, SMTP). It enables software to communicate over the network without dealing with lower‑level protocols.
6 – Presentation Layer
✚
Handles data translation, encryption, and compression. Ensures data from the Application layer is in a usable format for the receiver.
5 – Session Layer
✚
Manages dialogs (sessions) between applications, establishing, maintaining, and terminating connections.
4 – Transport Layer
✚
Provides end‑to‑end communication services for reliability, flow control, and error checking (TCP, UDP).
3 – Network Layer
✚
Determines routing and forwarding of packets across multiple networks (IP, ICMP).
2 – Data Link Layer
✚
Provides node‑to‑node data transfer, framing, and error detection (Ethernet, PPP, MAC addresses).
1 – Physical Layer
✚
Transmits raw bits over the physical medium (cables, signals, voltages, fiber optics).
Quick Comparison – OSI vs. TCP/IP
| OSI Layer | TCP/IP Equivalent |
|---|---|
| Application (7), Presentation (6), Session (5) | Application |
| Transport (4) | Transport |
| Network (3) | Internet |
| Data Link (2), Physical (1) | Link |