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Numbers and Names

Lesson 3 of 32 in Coddy's The OSI Model course.

Engineers usually say the number, not the name: "that's a layer 3 problem" or "an L7 load balancer". Translating instantly between numbers and names is the actual skill.

A classic mnemonic works bottom-up, one word per layer from 1 to 7: Please Do Not Throw Sausage Pizza Away (Physical, Data Link, Network, Transport, Session, Presentation, Application).

The three you will name most often in real work: 3 is Network (IP), 4 is Transport (TCP/UDP), 7 is Application (HTTP).

Challenge

Beginner

Print the layer number of each of these layers, one per line, in this order: Network, Transport, Application.

Expected output:

3
4
7

Try it yourself

Terminal

All lessons in The OSI Model

1Why Layers

The Layering Idea Seven LayersNumbers and NamesRecap - The Stack

4The Network Layer

IP and TTL Ping and ICMP Routing Tables Recap - Layer Three

7Encapsulation

Wrapping Data Headers Everywhere Reading a Capture Recap - Follow the Wrap

2The Physical Layer

Bits on a Wire How Long Will It Take Duplex and Collisions

5Transport: TCP and UDP

Ports The TCP Handshake TCP vs UDP Sockets in Action Recap - Layer Four

8The Journey of a Packet

A Click Happens Crossing the Networks Arriving and Climbing Recap - End to End

3Data Link and MACs

Frames and MACs Reading a MAC ARP Recap - Layer Two

6The Upper Layers

Session and Presentation The Application Layer Watching the Layers Recap - Top of the Stack

Practice on your own: Terminal playground