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The OSI model and other models represent a communication system as a stack of multiple layers. In this case we get a vertical structure where "user" is at the top and the receiver of communication at the bottom. What I have wondered for quite some time now is why we can’t represent the same thing as "stages" in a horizontal manner. There are multiple layers that we talk of in the OSI model where each has a different purpose and basically translates its input to something that the next layer will use. Depending on the protocol and the application under consideration we may have fewer than 7 layers or may even merge multiple layers into a single one.

My question is, where did this concept of a "stack" originate from where things are piled up vertically when talking of communication systems? We can also think of this process as a production line where our message goes through multiple stages, finally producing something that can be transmitted on the communication channel right? In this case we can represent the same system horizontally. Why does mankind use the word ‘stack’ and talk of it is a vertical structure when abstracting it?

JYelton
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quantum231
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  • 1) Communication is bi-directional; things go up and down the stack, so the one-directional conveyor doesn't map well. – pjc50 Sep 20 '13 at 14:16
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    2) Given a horizontal language, it's easier to arrange a set of labelled boxes vertically on the page rather than horizontally, hence a vertical bias to diagrams. (See "waterfall development", which arguably is much closer to your production line) – pjc50 Sep 20 '13 at 14:17
  • This question appears to be off-topic because it is about linguistics. The answer is that later technologies adapt the language of earlier ones, such as the construction of homes by building on top of earlier constructed foundations and our language in this reflects our need to reference the orientation of gravity. – RedGrittyBrick Sep 20 '13 at 15:47

2 Answers2

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When an OSI (or other) protocol stack is presented one aspect is that each layer on a system effectively talks to its peer layer on the other system. With the stacks vertical these layer-to-peer-layer relation is horizontal, which feels better than the alternative (vertical in your proposal).

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Another reason is that conceptually the lower layers are 'closer to the hardware', hence 'lower'.

In descriptions of other layered systems it often happens that one layer consists of independent parts, depicted side by side. Rotating such a picture 90 degrees does not feel right, probably because we want to talk about one layers as 'built on top of' another.

enter image description here

Wouter van Ooijen
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  • Its a circular argument to say we choose vertical stack because hardware is lower or because we want to write "built on top of". If our habit was horizontal organisation we'd justify it because hardware is leftmost and because it fits with "built to the right of" or "built after". – RedGrittyBrick Sep 20 '13 at 15:44
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    I hadn't thought before in terms of layers talking to the corresponding layers on the far end; that really helps clarify the meaning of the OSI model. In some cases I've dealt with from the perspective of small micros talking to PCs via custom protocols, the layer concept seemed rather murky (clean segregation of layers is a luxury that's not always available on small micros), but in more symmetrical cases it certainly seems helpful. – supercat Sep 20 '13 at 18:04
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Another perspective is that as humans, Stacking vertically denotes dependence on something else. Each layers in the OSI model depends on another layers at the bottom to perform its stack. Otherwise, the whole tower crumbles. Stacking horizontally doesn't denote dependance as strongly. Think of houses and other common human architectures.

Gustavo Litovsky
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  • aha, a moment of realization. I expected there certain level of understanding lies within the vertical structure itself. – quantum231 Sep 23 '13 at 10:07