I am really confused by how the layers these model work. I'm not asking about what are their functions. I read that transport layer provides end-to-end of all packet delivery, and networking also provides end-to-end of individual packets. What I am asking is does the transport layer delivers the packets all the way to destination and network layer does the same thing with individual packets? Do layers wait for the preceding layer to finish its job and then perform theirs, or they are not obligated and can run even if the preceding layer doesn't finish? And what does "end-to-end" actually mean? Thanks in advance!