*4.1. Implemented Architecture*

In order to implement the architecture depicted on the left of Figure 1, the components indicated in Figure 1 on the right were selected. As it can be observed at the bottom of the Figure, Android smartphones are used to read the Abbot's Freestyle Libre CGM sensor. If the patient is indoors, in an area where there is fog computing gateway deployed, the smartphone can communicate with it. Such a gateway is essentially a Single-Board Computer (SBC) that runs the required software. The smartphone can also send the collected values to other decentralized nodes on the Internet or to the Ethereum blockchain, which can be accessed by remote users. In addition, such users can access the data through a front-end that shows a user-friendly web interface. The following subsections describe in detail the characteristics, software and regular functioning of every component.
