You are viewing a free preview of this lesson.
Subscribe to unlock all 10 lessons in this course and every other course on LearningBro.
The Open Systems Interconnection (OSI) model is a conceptual framework created by the International Organization for Standardization (ISO) in 1984. It divides network communication into seven layers, each with a specific responsibility. Understanding the OSI model is essential for troubleshooting, designing, and discussing networks.
| Layer | Number | Name | Key Function | Example Protocols / Technologies |
|---|---|---|---|---|
| 7 | Application | Application | Provides network services to end-user applications | HTTP, FTP, SMTP, DNS, SSH |
| 6 | Presentation | Presentation | Data formatting, encryption, compression | SSL/TLS, JPEG, ASCII, UTF-8 |
| 5 | Session | Session | Manages sessions and connections | NetBIOS, RPC, PPTP |
| 4 | Transport | Transport | Reliable (or unreliable) end-to-end data delivery | TCP, UDP |
| 3 | Network | Network | Logical addressing and routing | IP, ICMP, ARP |
| 2 | Data Link | Data Link | Physical addressing and error detection | Ethernet, Wi-Fi (802.11), MAC addresses |
| 1 | Physical | Physical | Transmission of raw bits over a medium | Cables, fibre optics, radio waves |
Mnemonic (top-down): All People Seem To Need Data Processing
Mnemonic (bottom-up): Please Do Not Throw Sausage Pizza Away
The Physical layer deals with the raw transmission of bits (0s and 1s) over a physical medium.
| Medium | Type | Speed | Distance |
|---|---|---|---|
| Cat5e | Copper (Ethernet) | Up to 1 Gbps | 100 metres |
| Cat6a | Copper (Ethernet) | Up to 10 Gbps | 100 metres |
| Single-mode fibre | Fibre optic | Up to 100 Gbps+ | 80+ km |
| Multi-mode fibre | Fibre optic | Up to 100 Gbps | 500 metres |
| Wi-Fi 6 (802.11ax) | Radio | Up to 9.6 Gbps (theoretical) | ~30 metres indoors |
The Data Link layer handles communication between devices on the same local network segment. It uses MAC addresses (Media Access Control) for identification.
00:1A:2B:3C:4D:5E)| Sublayer | Name | Function |
|---|---|---|
| LLC | Logical Link Control | Flow control and error handling |
| MAC | Media Access Control | Physical addressing and frame transmission |
The Network layer is responsible for logical addressing and routing packets across different networks.
| Protocol | Purpose |
|---|---|
| IP (v4/v6) | Logical addressing and packet delivery |
| ICMP | Error reporting and diagnostics (e.g., ping) |
| ARP | Maps IP addresses to MAC addresses |
The Transport layer ensures end-to-end communication between applications on different hosts.
Subscribe to continue reading
Get full access to this lesson and all 10 lessons in this course.