I'm studying the OSI architecture model and I have doubts about the role of the SAP (Service Access Point). From what I'm getting it's an interface between the (N+1)-PDU and the (N)-SDU but does it also offer some sort of "virtual" connection between the same layers of two systems? Can you clarify this aspect?


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Each layer adds header during "send" operation. The corresponding layer in the destination (or next hop) reads the contents of that header during "receive" operation. We can see this as a virtual connection between layers of those two hosts.

Here is an image from Wikipedia illustrating this concept: https://en.m.wikipedia.org/wiki/File:OSI-model-Communication.svg

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