Hi @Fabio VIOLA ,
Welcome to Q&A forum!
Per my research, it seems that there is no official article on how to define a standard network diagram. Pease check if the following official articles are helpful. Thanks for your understanding!
Create a basic network diagram
Find more shapes and stencils
Import downloaded stencils
Besides, if you have any suggestions on Visio, it is recommended refer to this page to submit them to Microsoft directly.
Any updates, please let me know.
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