Spec & Goals 3 min
AQA Spec 3.5.2 — The concept of layers and the 4-layer TCP/IP model
By the end of this lesson you can:
- Explain why network communication is split into layers.
- Name the four layers of the TCP/IP model in order.
- State the role of each layer and which protocols sit in it.
Warm-Up 5 min
Last lesson you met lots of protocols. They don't all do the same job — they are organised into layers, each handling one stage of getting data from A to B.
Quick starter
Posting a parcel involves separate jobs: writing the letter, boxing it, addressing it, driving it. Why split one delivery into separate jobs?
Reveal the idea
Each job can be done and improved independently. Networks do the same: split communication into layers so each layer can be designed and changed without breaking the others.
Key Concept — four layers, four jobs 14 min
The TCP/IP model breaks network communication into four layers. Each layer has a specific job and talks only to the layers directly above and below it.
| Layer | Job | Example protocols |
|---|---|---|
| Application | Provides services to the user's programs (e.g. web, email, file transfer). | HTTP, HTTPS, FTP, SMTP, IMAP |
| Transport | Splits data into packets and reassembles them in order; checks delivery. | TCP |
| Internet (Network) | Adds IP addresses and routes packets across networks. | IP |
| Link (Network access) | Handles the physical hardware connection that actually moves the bits. | Ethernet, Wi-Fi |
Worked Example — which layer? 12 min
Problem: For each protocol/job, name the TCP/IP layer it belongs to.
| Protocol / job | Layer |
|---|---|
| HTTPS loading a secure web page | Application |
| Splitting a file into packets and numbering them | Transport (TCP) |
| Adding the destination IP address and routing | Internet (IP) |
| Sending the bits over the office Ethernet cable | Link |
| SMTP sending an email | Application |
Answer pattern: user-facing protocols (HTTP/S, FTP, SMTP, IMAP) → Application; packets → Transport; IP addressing/routing → Internet; physical Ethernet/Wi-Fi → Link.
Try It Yourself 12 min
Goal: List the four TCP/IP layers in order, top to bottom.
Goal: State which layer each of these belongs to: HTTP, TCP, IP, Wi-Fi.
Goal: Explain one advantage of organising network communication into layers.
Hint: think about changing one part without breaking the rest.
📝 Exam Practice 10 min
State the four layers of the TCP/IP model in the correct order.
Mark scheme
- Application (1)
- Transport (1)
- Internet / Network (1)
- Link / Network access (1)
- (Order top-to-bottom required for full marks.)
Identify the layer that uses (a) TCP and (b) IP.
Mark scheme
- (a) TCP — Transport layer (1).
- (b) IP — Internet / Network layer (1).
Explain one benefit of using a layered model for networking.
Mark scheme
- Each layer can be developed / changed independently (1).
- Without affecting the other layers / it breaks a complex task into manageable parts / aids standardisation between manufacturers (1).
Recap & Key Terms 3 min
Networking is split into layers so each job is handled separately. The TCP/IP model has four: Application (HTTP/S, FTP, SMTP, IMAP), Transport (TCP — packets), Internet (IP — addressing/routing) and Link (Ethernet, Wi-Fi). Data goes down the layers to send and up them to receive.
- Layer
- A division of network functions; each performs one role using its own protocols.
- Application layer
- Provides network services to user programs — HTTP, HTTPS, FTP, SMTP, IMAP.
- Transport layer
- Splits data into packets and reassembles them — TCP.
- Internet layer
- Adds IP addresses and routes packets across networks — IP.
- Link layer
- Manages the physical connection that moves the bits — Ethernet, Wi-Fi.
Homework 1 min
Task (≤ 15 min): Draw the four-layer TCP/IP model as a stack. Label each layer with its job and one example protocol.
Model answer
Top to bottom: Application (services for programs — HTTP), Transport (packets & reassembly — TCP), Internet (addressing & routing — IP), Link (physical connection — Ethernet/Wi-Fi).
Award marks for: four layers in correct order (2); a correct job for each (1); a correct example protocol for each (1).