Network Model Abstractions

I’m working through the Cloud Foundations certification curriculum currently. And in section 6.1.2 “Identifying OSI model layers” there were some charts that dealt with the OSI model, but I noticed things were different. I did the CCENT curriculum last term where the 7 OSI layers are reduced down to 4 because the TCP/IP stack only uses 4 logical layers, and wanted to see how the ‘new’ changes all work compared to the older model I learned originally.

All of us geeks have our own way of understanding the 7 OSI layers and how they map onto real world troubleshooting. And how the TCP/IP model simplifies it for the specific use-case of networking TCP/IP packets with the effect of reducing the 7 layers down to 4. But I think it would be useful to have one list that puts all these ‘Communication Layer Abstractions’ together.

The mnemonic I learned to keep the OSI layers straight long ago was: All-People-Seem-To-Need-Data-Processing and to parse out the layer name from that. Whatever name we give the layer, there just seems to be a natural escalation of data qualities as it works it’s way up a network stack.

The change I mentioned is in layers 4 and 5 between this table and 4 and 5 in other models. Now 4 is understood to be all about segments, but used to be “End-to-End Connection and Reliability”. Which then moves the logical job of maintaining a connection fully to layer 5 which used to be understood as “Interhost Communication”.

All in all it makes good sense to me. And just to drill home the sequence of layers and the qualities they provide to the stack, as an exercise I made this chart.