Open System Interconnection (OSI) model diagram.

Mnemonic For OSI Model Layers

There are a million acronyms out there to help students remember the layers of the Open Systems Interconnection (OSI) model. Why offer another? Well, this one has worked best for me.

As a reminder, the OSI Model Layers are as follows:

  • Layer 7: Application
  • Layer 6: Presentation
  • Layer 5: Session
  • Layer 4: Transport
  • Layer 3: Network
  • Layer 2: Data Link
  • Layer 1: Physical

AP(p)S Transport Network Data Physical(ly)

I like this because it helps me remember several important pieces of information in one tidy little phrase.

  1. The Transport, Network, Data (link), and Physical layers are spelled right out.
  2. Grouping Application, Presentation, and Session together into the acronym AP(p)S helps group the upper layers together, and it conveys that these layers are of primary concern for the application-level data.
  3. The sequence of the operations in terms of wrapping the layers starts with the top (layer 7: App.) All to often, I hear people say they are confused about the layers because layer one seems like it should be wrapped by the other layers. This mnemonic helps avoid that issue. Additionally, the layers read naturally from top to bottom when I see them represented, and this order makes writing them down more natural.
  4. Finally, the phrase reminds me that these abstractions all rest on a physical communication layer (i.e., when troubleshooting, start there first!)

If this helps you, great, and if not, I hope you find a mnemonic that works well for you 🙂






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