OSI Model — Packet Encapsulation

L7 · ApplicationData

Your actual message (e.g. an HTTP GET request)

L6 · PresentationData

Encryption & formatting (TLS, character encoding)

L5 · SessionData

Manages the dialog between the two hosts

L4 · TransportSegment

Adds source/dest ports + sequence numbers for reliability

L3 · NetworkPacket

Adds source & destination IP addresses for routing

L2 · Data LinkFrame

Adds MAC addresses + an error-checking trailer (FCS)

L1 · PhysicalBits

The frame becomes electrical/optical/radio signals on the wire

The Packet, Being Wrapped

Press "Send Data" to watch each layer add its header.

OSI Model Explained — Interactive Packet Encapsulation

The OSI model is easier to understand when you watch it happen. This simulator sends a message down the seven layers and shows each layer wrapping the data in its own header — so you can see encapsulation, the changing PDU names (Data → Segment → Packet → Frame → Bits), and what each header actually adds.

What you can do in this simulation

Press Send and watch your data travel down all seven OSI layers
See the packet grow as each layer adds its header (encapsulation)
Learn the PDU name at each layer: Segment, Packet, Frame, and Bits
Read what each header adds — TCP ports, IP addresses, Ethernet MAC + trailer
Understand that the receiver reverses the process (decapsulation) going back up the stack

Concepts covered

OSI model · encapsulation · network layers · PDU · TCP/IP model · headers · protocol stack

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