2. The Problem

Here is the issue as shown in the picture below

Consider that a number of devices are networked and need to exchange data with one another. These are connected as a local network. They also want to exchange data with other networks across the internet.

How to do this?

Well, the very simplest thing to do would be to give each one a unique identity in the form of a number. For example the green device could be called '1', the orange '2' and the blue '3'. Then they could swap information by attaching the correct address to each piece of information being exchanged.