Network Layers and the Protocol Stack
A network is split into layers, each with one job and each talking only to the layer above and below: application, transport, internet, link. A message gains a header at each layer on the way down and loses it on the way up.
What a learner can do afterwards
- Say which layer a named protocol belongs to and what that layer is responsible for
- Follow a message down the stack at the sender and back up at the receiver
- Explain what the split buys: one layer can change without the others being rewritten
1 · Read
A network splits into layers, each with one job and each talking only above and below. You meet four: application on top, then transport, then internet, then link at the bottom. HTTP lives at application, TCP at transport keeping delivery reliable, and IP at internet finding paths. The split is why a photo you send still arrives when the WiFi below changes.
Follow one message out and back. Going down the sender stack, each layer adds its own wrapping before passing down. Coming up at the receiver, each matching layer strips and checks its wrapping, until the app gets clean data.
The split buys independence: one layer can change without rewriting the rest. New cables or WiFi can arrive while web pages work untouched. Reliability also stays local: if a packet vanishes, only the delivery layer notices and resends it, while the app above stays simple and the wires below stay dumb.
You place a protocol by asking its job. Moving bits is link, finding paths is internet, keeping flows smooth is transport, and serving people is application. Naming the job names the layer.
Each layer wraps going down, unwraps going up, and changes without disturbing neighbours.
2 · Watch
Take it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.