There is another famous ‘stack’ of notions—the ‘OSI model’ which describes seven abstraction layers to connect two computers via facilities typically provided by telephone companies in the 80’s. I believe that it was good computer science to elaborate details of those layers and thus give names and precise descriptions of important communication functions, and at the same time a concrete way of providing them. Yet that particular ordering was to a degree arbitrary and not always optimal. Some took the OSI model as received wisdom and were thus blind to the alternatives. Some networks have profitably permuted layers 3, 4 and 5. To gain the obvious benefits of interoperability one need agree on details of several abstract services, at different levels. This does not require uniform adherence to the entire stack.