Knowledge Organiser: TCP/IP Layers
Key Terms
- TCP/IP model: A four-layer framework describing how data is transmitted over the Internet
- TCP: Transmission Control Protocol — reliable delivery with error checking and retransmission
- IP: Internet Protocol — handles addressing and routing of packets across networks
- Encapsulation: Each layer adds its own header as data passes down the stack
Must-Know Facts
- Four layers (top to bottom): Application, Transport, Internet, Link
- Application layer: HTTP, HTTPS, FTP, SMTP, DNS — what the user interacts with
- Transport layer: TCP (reliable) — manages end-to-end delivery
- Internet layer: IP addresses, routing across networks
- Link layer: Ethernet/WiFi, MAC addresses, physical transmission
- Data travels DOWN the layers when sending, UP when receiving
- TCP = reliable (resends lost data); IP = addressing and routing
Key Concepts
- Application layer: Provides network services to applications (HTTP for web, SMTP for email)
- Transport layer: TCP breaks data into segments; checks for errors
- Internet layer: Adds IP addresses (source and destination); routers use this to forward packets
- Link layer: Adds MAC addresses; handles physical transmission over cables or WiFi
- TCP for accuracy: web pages and email need every piece of data to arrive correctly, so they use TCP
Common Mistakes
- Getting the layer order wrong: The four layers top to bottom are Application, Transport, Internet, Link — confusing Internet and Transport layers is very common
- Confusing TCP and IP: TCP makes delivery reliable, with error checking and retransmission; IP handles addressing and routing
- Saying IP addresses are at the Transport layer: IP addressing and routing happen at the Internet layer — the Transport layer handles reliable end-to-end delivery (TCP)
- Confusing MAC addresses and IP addresses: MAC addresses operate at the Link layer (physical hardware identification); IP addresses operate at the Internet layer (logical network addressing) — they serve different purposes
- Forgetting encapsulation: As data passes down the stack, each layer adds its own header — this process is called encapsulation and must be mentioned when describing how the TCP/IP model works