Lesson 1.6: Layered models: OSI and TCP/IP
Why networking is split into layers, the seven layers of the OSI model and the four of the TCP/IP model, what a protocol is, and encapsulation: each layer wraps the data of the layer above. In the lab you find a trace of each layer on your own laptop (the hardware address, the IP address, a listening port, an HTTP answer), then read a captured web request in which you can see all of them at once.
18 min
You will learn to
- Define a protocol and a layer
- Name the seven OSI layers and the four TCP/IP layers
- Explain encapsulation
- Match addresses, ports and protocols to their layers
- Read a simple packet capture
Key terms
- Protocol
- An agreed set of rules for how two parties exchange messages: format, order, meaning.
- Layer
- One level of a network model that does one job and offers a service to the layer above.
- OSI model
- A seven-layer reference model: 1 physical, 2 data link, 3 network, 4 transport, 5 session, 6 presentation, 7 application.
- TCP/IP model
- The four-layer model the internet actually uses: link, internet, transport, application.
- Encapsulation
- Each layer wraps the data from the layer above with its own header, like a letter put in an envelope, put in a box.
- MAC address
- The hardware address of a network card, used only inside a local network.
- Port
- A number from 0 to 65535 that identifies a program or service on a host.
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