\section{Environment}\label{env}

The research presented in this paper was mainly driven by \textit{Magrathea Laboratories e.V.} \cite{maglab}, the local hackerspace in Fulda, Germany, in cooperation with researchers at the department for computer science at Fulda University of Applied Sciences.
Requirements were clearly defined by Magrathea Laboratories' demands to provide local and remote control over various sensors and actors in the foundations rooms to visitors and members.
Such components include door sensors, power sockets, temperature sensors, projectors and screens who are all managed by a home-automation controller, which is driven by the software \textit{home-assistant} \cite{HASS}.
It provides direct control over all existing components using a web-based user interface and allows to define rules and automations on how these components interact.

For the component's hardware, boards based on the \textit{ESP8266} micro-controller are used.
These boards feature a small and robust design, achieve very low power consumption and integrate WiFi without requiring any extra components.
It integrates a Tensilica L106 32-bit micro controller unit (MCU) with a maximum CPU performance of 160 MHz, 64 kB instruction memory and another 96 kB of main memory. 
According to the manufacturer, the ESP8266 is among the most integrated WiFi-capable chips in the industry.
While at the beginning of this research, mostly \textit{ESP-01s} \cite{ESP-01s} boards in combination with self-developed power supplies and use-case specific hardware components were deployed, we quickly integrated \textit{Sonoff} \cite{sonoff} wireless smart switches product series offered by \textit{ITEAD}.

The firmware for all of the \textit{ESP8266}-based devices in the hackerspace is based on our common software platform, referred to as \textit{ESPer}.
\textit{Sming}, which in turn is based on the open-source SDK for \textit{ESP8266}, provides the base library for this framework.
It integrates a lot of other software components and provides all kinds of functionality shared by all devices, allowing to reuse parts of the source code in multiple devices.

For communication with the controller, the \textit{MQTT} \cite{MQTT} protocol is used.
It provides a lightweight messaging mechanism implementing the publish-subscribe pattern that allows devices to listen for commands and publish their current state to the controller and other interested parties.
The controller software has out-of-the-box support for this protocol, which allows easy integration of all different device types using the same patterns.

The components all share the same configuration in regard to the network access and the controller to communicate with.
The configuration is provided during build time, which eschews the need for a configuration interface and reduces the management overhead, thus minimizing security leaks.