The OSI Model describes how data travels across a network. (Photo credit: Thomas Jensen)
The Open Systems Interconnection (OSI) Model is a framework describing how network devices transmit and use data. It consists of seven layers, as seen and briefly described here:
Layer 7: Application (a user interacts with the data)
Layer 6: Presentation (data is translated between application and the network)
Layer 5: Session (devices are synced up so they can communicate)
Layer 4: Transport (data is classified as segments via reliable TCP or as datagrams via fast UDP)
Layer 3: Network (logical routing is determined via the shortest and/or most reliable path using IP addresses)
Layer 2: Data link (physical addressing is determined using MAC addresses)
Layer 1: Physical (data is physically sent over binary via electrical signals)
How to Memorize the OSI Model
To memorize the order of the OSI layers, it can be helpful to use mnemonic devices such as:
Layers 7 to 1:
All people seem to need data processing.
APS transports network data physically.
Layers 1 to 7:
Please do not throw sausage pizza away!
Please do not touch Steve’s pet alligator!
More Resources
This guide just scratches the surface of defining the OSI Model. For more in depth understanding, check out these resources!
NetworkChuck video demonstrating how the OSI Model works on YouTube.
Professor Messer video explaining the OSI Model.
TryHackMe room walking you through the OSI Model with questions and answers (subscription required) with a game at the end!
Thanks for reading!