How to use the OSI Model Interactive Reference
- 1. Click a layerSee its job, data unit, protocols, devices and TCP/IP equivalent.
- 2. Walk through encapsulationFollow a web request down the stack.
- 3. Take the quiz8 random 'which layer?' questions with instant answers.
The seven layers
- Physical: bits as signals on cables, fibre or radio. Hubs and repeaters.
- Data link: frames between devices on the same network, using MAC addresses. Ethernet, Wi-Fi and switches.
- Network: packets routed across networks with IP addresses. Routers.
- Transport: end-to-end delivery between programs using ports. TCP for reliable streams, UDP for fast datagrams.
- Session: setting up and ending conversations.
- Presentation: formats, encryption (TLS) and compression.
- Application: what apps talk: HTTP, DNS, SMTP and SSH.
The internet actually runs on the simpler TCP/IP model, which merges layers 5–7 into Application and layers 1–2 into Network access. The OSI model is still the standard way to describe and troubleshoot networks, and a regular interview topic.
Worked example: opening a web page
When your browser requests a page over HTTPS, data moves down the stack, and each layer adds its own header:
- Application: the request
GET /index.html HTTP/1.1, encrypted by TLS. - Transport: a TCP header with ports, such as 51514 → 443.
- Network: an IP header with source and destination IP addresses.
- Data link: an Ethernet header with MAC addresses, plus a checksum at the end.
- Physical: the whole frame as 1s and 0s on the wire or radio.
The server unwraps them in reverse order. Remember the order top to bottom with "All People Seem To Need Data Processing". When something breaks, troubleshoot from the bottom up: is the cable in (1), is there a link (2), is there an IP address (3), is the port open (4)?
Frequently asked questions
Is TLS at layer 6 or 7?
It doesn't fit neatly. Exams usually place encryption at layer 6, Presentation; in practice TLS sits between TCP and the application.
Which layer does a switch work at?
Layer 2, using MAC addresses. Layer 3 switches can also route by IP address.
How is OSI different from TCP/IP?
OSI has 7 layers and is a reference model; TCP/IP has 4 and is what the internet actually uses.
Is the osi model interactive reference free to use?
Yes, the osi model interactive reference is free and costs nothing. Seeing your first quiz score shows a short form for your name and WhatsApp number one time; once that's done, this tool and every other Uncodemy tool open with no form.