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OSI Model Layers

The Open Systems Interconnection model describes how data moves from an app on your screen down to the electrical signals in the wire.

🧪 Encapsulation Lab Interactive

7 Application Data
6 Presentation Data
5 Session Data
4 Transport Segment
3 Network Packet
2 Data Link Frame
1 Physical Bits
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Layer 7: Application

What it does: This is what you see. It creates the data and talks to the user.

HTTP SMTP SSH

Layer 6: Presentation

What it does: Formatting, encryption, and compression. It translates data into a readable format.

SSL/TLS JPEG ASCII

Layer 5: Session

What it does: Starts, keeps, and ends the conversation between devices.

API Sockets WinSock

Layer 4: Transport

What it does: Reliability and error checking. Chops data into "Segments".

TCP UDP Ports

Layer 3: Network

What it does: Addressing and Routing. Moves "Packets" between different networks.

IP Address Routers ICMP

Layer 2: Data Link

What it does: Physical addressing. Moves "Frames" between devices on the SAME network (Switching).

MAC Address Switch
🔍 What is a VLAN?
Virtual LAN. It logically separates network segments within the same physical switch. It improves Security (HR can't see Engineering traffic) and reduces Broadcast Domains.

Layer 1: Physical

What it does: Sending raw bits (1s and 0s) over a physical medium.

Cables Wifi Hubs