Logical (horizontal) vs real (vertical) communication
Network Architecture I · S1.2 · Every entity believes it exchanges its PDU directly with its peer. None of them does.
Point of view of layer:
What the layer perceives
What is happening right now
Example:Highlight:
The three words
This is the frame leaving A. Click a piece: who wrote it, and who is going to read it?
Who writes it and who reads it
Everyone else
Keyboard: 123 switch view · ←→ step · space play/pause · ↑↓ change layer (view 1) · R open/close the black box
About this visualization
Explains in three views that communication between peer layers is only logical and that the only thing actually transmitted is signals over the physical medium. The first animates a PDU between a Wi-Fi host, a router and an Ethernet host: the student picks each layer's point of view, opens the black box of the underlying service and can segment a 4000-byte message into three TCP segments. The second tells service, protocol and interface (SAP) apart step by step and lets the student swap the layer's protocol. The third shows which entity writes and which reads each header of the frame.