The TCP/IP Model Without the Acronym Soup

The layered model, finally intuitive: each layer does one job and trusts the layer below, like nesting envelopes - Link, Internet, Transport, Application, plus TCP vs UDP and a packet's round trip.

1. Why Layers? Each network layer does one job and trusts the layer below it - like nesting a letter in envelopes, where the writer ignores the trucks and the trucks ignore the words. That wrapping is called encapsulation.
2. The Four Layers Link gets data to the next hop, Internet (IP) addresses and routes it across networks, Transport (TCP/UDP) delivers it to the right program, Application (HTTP/DNS) is what you actually use - mapped onto one real web request.
3. TCP vs UDP & a Packet's Round Trip TCP is reliable, ordered, and connection-based (the handshake); UDP is fast and fire-and-forget (video, games, DNS). Then: one packet traced down the stack on send and back up on receive - plus the OSI-7-vs-TCP/IP-4 confusion, settled.