## 3 System Description and Main Components
### The Physical World  
The IoTMADLab is a physical space designed to work with various teams, IoT devices, and protocols to develop a standardized IoT network reference architecture. This architecture aims to establish an open, neutral, and interoperable IoT network that facilitates the  
Figure 2: Main building blocks for the Digital Twin implemented for the controlled environment at IoTMADLab. Black arrowed lines highlight the communication channels, and they are labeled with the employed protocols or means. direct connection of devices from different manufacturers within the same service, as well as direct connectivity with devices from other services and manufacturers. To achieve this, it mainly consists of an integration and testing laboratory and a pilot installation area. In the laboratory, a series of technical tests are conducted to verify the connectivity and interoperability of devices linked to various IoT sensors and actuators. The pilot installation areas comprise a controlled real-world environment where equipment, whose interoperability has been previously verified in the laboratory, is deployed. In this area, their performance under real conditions is tested, monitored, and the impact of interoperability on city services is assessed. Figure 3 presents the IoT laboratory and two areas of the controlled environment of the IoTMADLab. The controlled environment encompasses diverse urban elements that are equipped with IoT devices enabling the digitalization interface (sensor/actuator) and the communications to the Internet:  
* Streetlights: there are 12 LED streetlights from different manufacturers, each one equipped with IoT nodes, illumination, and motion detection sensors (from different vendors). The IoT nodes are connected through a Zhaga interface, allowing plug&play replacement, while sensors use both Zhaga and internal interfaces. The streetlights can work autonomously, being triggered by illumination and motion/presence values, controlled manually (with remote control commands), or depending on values from other sensors following pre-configured rules. * Parking lots: there are four parking lots equipped with IoT parking sensors, both below and above ground. The sensors, which are battery-powered, detect if a vehicle stands at parking lot by means of radar and earth magnetism sensors. When a change in the parking status is detected, the device sends a message indicating the new status. To save battery, these sensors remain in sleep mode most of the time, waking up periodically to check the parking occupancy or to send a periodic keep alive message if there is no change in the parking status. * Waste containers: there are two garbage disposal bins and a public paper recycling container equipped with waste IoT sensors. The devices, which are radar-based volumetric sensors, measure the filling level of the bins/containers. These devices also have GPS to generate alarms in case of detecting large movements with respect to the installation location, a temperature sensor with configurable thresholds to generate alarms in the event of fire, and accelerometers to detect emptying operations and alarms due to vandalism. These devices are battery powered and will provide up to eight years of operation depending on how frequent measurements and transmissions are configured. * Environmental information: different IoT sensors monitor environmental parameters such as outdoor temperature, relative humidity, wind speed, and solar radiation. They are connected to the electrical mains and allow both periodic measurement and data request. * Watering systems: three irrigation valves regulate water flow for green areas watering, which may be scheduled depending on weather forecast and actual soil moisture values. Soil temperature and pH sensors provide additional information. Both irrigation valves and soil sensors are plugged to IoT nodes to enable communications. * Building facilities: the IoTMADLab indoor laboratory activities are monitored and optimized using diverse IoT devices.