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The highest "layer" built on Bitcoin will be defined as the "application" layer. However, whether it ends up being the 3rd, 4th, or 5th layer etc. is still TBD. All layers sitting below the application layer will be defined as infrastructure layers. This is similar to the current internet stack, which consists of a link layer, a network layer, a transport layer and followed by an application layer (the highest layer).
Prior to Lightning and other 'layer-2s', all that existed was the Bitcoin basechain. At that point in time, the layer-1 blockchain was the application layer, enabling participants to transact with one another. However, the creation of the Lightning network brought another infrastructure layer to Bitcoin, adding additional functionality, beyond just transacting value.
Each incremental infrastructure layer should improve the functionality and potential number of applications that can be built on Bitcoin. Once the the marginal utility from adding infrastucture layers approaches zero, no more layers will be added. At this point, we'll be able to define what the ultimate "application layer" on Bitcoin will be.
Maybe it will be layer 3 or 4, however, there is no reason to think that it couldn't be layer 6, 7 or 8. Only time will tell...
HAHA. I'm sure that OSI will invent at least 7 when it goes fully mainstream. I think you can say that the same logic applies even to internet OSI layers, in that first there was the link (point to point) then there was IP, then TCP, and at first HTTP was an application layer.
Really, whatever is implemented by an application is the application layer. Applications can be built on top of other applications, so the distinction becomes a bit vague.
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Agreed, distinction will always be vague.
If we are forced to put structure around it though, I think that framework is reasonable, despite its flaws.
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Yeah, it just gets out of date as people keep stacking more things on top of what was previously called "application" as they interop them and the upper layers of the cake get more and more indistinguishable.
I think that really, even TCP/IP, as a network layer, is an application. How can you say that netcat is not an application? Or telnet, both of which sit directly above TCP/IP. Indeed, TCP is on top of IP, in fact, it's an application for reliable message transport. The network itself is an application!
Anyhow, la la la la so boring the grandstanding of academics who didn't invent the protocols to make pronouncements about other people's work.
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