---
title: "Network Layers and the Protocol Stack"
description: "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"
canonical: https://lightmysky.com/learn/computing/network-layers-and-the-protocol-stack-mt_O3Ew6c2ynD
source: https://lightmysky.com/learn/computing/network-layers-and-the-protocol-stack-mt_O3Ew6c2ynD.md
retrieved: 2026-09-12
---

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# 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.

Subject: Computing · Area: Computer Systems · Ages 17 to 18
Page: https://lightmysky.com/learn/computing/network-layers-and-the-protocol-stack-mt_O3Ew6c2ynD

## Ready when they can

- 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

## Lesson: Layers that carry your message

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.

**Example.** 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.

**Recap.** Each layer wraps going down, unwraps going up, and changes without disturbing neighbours.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Packets and Protocols on a Network](https://lightmysky.com/learn/computing/packets-and-protocols-on-a-network-mt_IffXVDtfLX)

## Opens up

- [Layering and Encapsulation in the Protocol Stack](https://lightmysky.com/learn/computing/layering-and-encapsulation-in-the-protocol-stack-mt_D33SEBslXH)
- [IP Addressing and How Routers Choose a Path](https://lightmysky.com/learn/computing/ip-addressing-and-how-routers-choose-a-path-mt_l0dRGocXGw)