Networking
Cheat sheet
OSI Model on One Card: Layers, PDUs, Devices
OSI on one card: can you name all seven layers before I do?
Quick check · tap an answer to continue
Lesson notes
Key points
- 7 layers, top-down: Application, Presentation, Session, Transport, Network, Data Link, Physical: say them first.
- Transport: segment: Layer four's data unit is the segment, handled by TCP or UDP using ports.
- Network: packet: Layer three's unit is the packet, routed between networks by IP addresses.
- Data Link: frame: Layer two's unit is the frame, delivered locally by switches using MAC addresses.
- Physical: bits: Layer one moves raw bits as signals over copper, fibre or radio.
- Encapsulation order: Sending adds headers going down: data, segment, packet, frame, then bits.
Takeaway: Segment, packet, frame, bits: layers 4, 3, 2, 1.
Quick check: At which OSI layer is data called a frame and forwarded by MAC address?
- Network layer
- Data Link layer
- Transport layer
Layer 2, Data Link, uses frames and MAC addresses, handled by switches.
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