Automating Manufacturing Systems - Process Control and ...

plc network - 28.3
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Figure 28.2
The Tree Topology
28.1.2 OSI Network Model
The Open System Interconnection (OSI) model in Figure 28.3 was developed as a
tool to describe the various hardware and software parts found in a network system. It is
most useful for educational purposes, and explaining the things that should happen for a
successful network application. The model contains seven layers, with the hardware at the
bottom, and the software at the top. The darkened arrow shows that a message originating
in an application program in computer #1 must travel through all of the layers in both
computers to arrive at the application in computer #2. This could be part of the process of
reading email.