Submitted by netdesign on
What are the OSI layers? For many years the OSI model (Open Systems Interconnection Model) has described the layers of information in a network, particularly the low-level transport mechanisms. From top to bottom, these are the layers and how these layers relate to your product design.
Ethernet is physical layers: layers 1 and 2. TCP/IP (Transmission Control Protocol / Internet Protocol) is a protocol, not a network, and uses layers 3 and 4.
| Layer | Name | Function | Example |
|---|---|---|---|
| 7 | Application | Meaning of data | HTTP |
| 6 | Presentation | Building blocks of data and encryption | |
| 5 | Session | Opening and closing of specific communication paths | |
| 4 | Transport | Error checking | TCP, UDP |
| 3 | Network | Determination of data paths | IP |
| 2 | Data link | Data transmission, source, destination | Ethernet |
| 1 | Physical | Voltage levels, signal connections, wire, or fiber | RJ45, fibre optique |
A comparison with the ISO layers
Let’s compare the OSI layers with a road. A man go from office to home with a taxi on the motorway.
Layer 1 (physical layer) = The roads
Layer 2 (Data link) = Source is the office; destination is home.
The MAC address is the unique registration number of the car.
Layer 3 (Network) = Determination of the correct road to take; the IP address is the street address. Same address may be found in several towns.
Layer 4 (Transport) = Error checking: is the destination correct?
Layer 5 (Session) = pay fare; handshake between source and destination
Layer 6 (Presentation) = The taxi is one of many on the road – 1 message in the datastream
Layer 7 (Application) = What is the purpose of travel? The passenger in the taxi is the purpose of the message, which also includes the source and destination information
