If you spend any amount of time at all dealing with networking design or implementation issues, or learning about how the various protocols operate, the names and numbers of the various layers will eventually become “second nature”. Trust me, I know this from experience!

Many people, however, especially those just learning about networks, find it difficult to recall the names of all the layers, and especially, what their exact order is. To help these people, a number of mnemonics (pronounced “neh-MON-iks”—another wonder of the English language) have been created as memory aids. These are cute phrases where each word starts with the first letter of an OSI model layer, arranged in the correct order.

I have seen a few of them in my time, some of which go in ascending layer number order, and some of which go in the other direction. These two go from physical layer to application layer:

• Please Do Not Throw Sausage Pizza Away
  
  
• Please Do Not Touch Steve's Pet Alligator

And these ones go the other direction (application to physical):

• All People Seem To Need Data Processing (this is a popular one)
  
  
• All People Standing Totally Naked Don't Perspire (hmm, that's interesting…)

For your convenience, I have illustrated all four of these in Figure 18.

Oh, and here's one I just made up: All People Should Teach Networking Daily Please.

(Well, I like it! J)