Envelopes inside envelopes
Layered networking works by encapsulation: each layer wraps the data from the layer above in its own header (and L2 adds a trailer too), so by the time your request leaves the antenna it's a frame nested several headers deep. Every header serves exactly one layer's job and is read only by its peer at the far end — ports for the transport demux, addresses for end-to-end routing, MACs for the local hop, and the FCS for error detection.
This lab wraps a real HTTPS request step by step, showing the packet on the wire growing, the PDU name changing at each layer, and the key fields each header carries. It's the bridge from Wi-Fi to the rest of networking: the 802.11 frame you met in the security plates is just the L2 wrapper, swap it for Ethernet and everything above is identical. Knowing which header owns which field is the entire skill of reading a capture — and of deciding which layer (and which team) owns a problem.