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2. The Simplest Network > Layers of Agreement

Layers of Agreement

Before you can get things to talk to each other, you have to lay some ground rules for the communication between them. These agreements can be broken down into five layers, each of which builds on the previous ones:

• Physical

How are the physical inputs and outputs of each device connected to the others? How many connections between the two devices do you need to get messages across?

• Electrical

What voltage levels will you send to represent the bits of your data?

• Logical

Does an increase in voltage level represent a 0 or a 1? When high voltage represents 1 and low voltage represents 0, it’s called true logic. When it’s reversed—high voltage represents 0 and low voltage represents 1—it’s called inverted logic. You’ll see examples of both in the pages that follow.


  

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