Overview
the OSI (Open Systems Interconnection) model is a framework that describes the broad overview of how data transverses our systems. It divides networking into 7 layers, each with different responsibilities
layer summary:
| layer | name | description | example |
|---|---|---|---|
| 7 | application | layer we see - network services to end users | HTTP, FTP, DNS, POP3 |
| 6 | presentation | character encoding, application encryption- combines with application layer | SSL/TLS |
| 5 | session | Manages communication between devices | control protocols, tunnelling protocols |
| 4 | transport | transport from one device to another | TCP, UDP |
| 3 | network | routing and addressing | IP addresses, routers, packets |
| 2 | data link | physical addressing, switching, data link control protocols | MAC address, frames, switches |
| 1 | physical | signalling, cabling, connectors | cables, fibre, connectors, electrical signals |
How to remember layer order:
All People Seem To Need Data Processing
(layer 7 to layer 1)
Layer details:
Layer 1 - Physical
- Role: signalling, cabling, connectors
- examples: cables, fibre optics, electrical signals
Layer 2 - Data Link
- Role: data link control protocols (MAC) - "switching layer"
- Examples: Frame, MAC address, EUI-48, EUI-64, switches
Layer 3 - Network
- Role: routing, logical addressing, fragmenting frames to traverse different networks - "routing layer"
- Examples: IP addresses, routers, packets
Layer 4 - Transport
- Role: transport from one device to another - "post office"
- Example: TCP, UDP
Layer 5 - Session
- Role: communication management between devices
- Example: control protocols, tunnelling protocols
Layer 6 - presentation
- Role: character encoding, application encryption - combines with the application layer
- Examples: SSL/TLS
Layer 7 - Application
- Role: the layer user directly interacts with - provides network service to the user
- Examples: HTTP, FTP, DNS, POP3
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