Page 43 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 5 – Internet of Everything

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 5

3.1 MQTT OpenHAB

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MQTT is a publish&subscribe network broker‑based Home Automation open‑
messaging protocol, which is used to transport messages sour pr home application platform used t run
between devices in IoT networks or, in general, in con‑ homes. It naivel man devices al‑
strained scenarios. Note that it is largely used in the IoT low user t further ext capabilities b in‑
domain thanks to its robustness and power‑saving com‑ stalling modules and plugins. Moreover, OpenHAB allows
munication. MQTT is based on two types of entities: mes‑ the writing of custom logical rules, which can be triggered
sage broker and clients. In more detail, a one‑to‑many using deployed sensors and perform user‑de ined actions
message distribution is performed as well as another fea‑ (e.g., turn on lights on a given time or when a motion sen‑
ture involved in the decoupling of information between sor is activated). OpenHAB makes use of various differ‑
sources and consumers. In general, MQTT is agnostic ent concepts to model the smart home environment, two
about the content of the payload. The broker can be im‑ of which are relevant for the case study presented in this
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plemented by using Mosquitto , but other solutions are paper:
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also available, such as HiveMQ .
• Things can be seen as entities that can be physically
The concept of topic is fundamental in MQTT; it consists added to the system, like a vendor sensor gateway,
of strings used by the broker to ilter messages gathered or virtual, like a web service which can provide in‑
by the connected client; a topic has one or more levels, formation to the system
separated by a forward slash, so as to obtain a logical
• Items, instead, represent functionality used by the
tree structure. Topics are used by clients for publishing
application. For example, the temperature values
messages and for subscribing to the updates from other
read by a sensor, or the current state of a switch,
clients, thus avoiding a continuous polling among produc‑
are considered as items; while the sensor itself is the
ers and consumers. There is the possibility to subscribe
things which provides such items.
to an exact topic or to multiple topics at once by using the
wildcards, represented by the following symbols: (i) + for For logical operations, OpenHAB uses rules, which are
a single‑level wildcard (i.e., exactly one topic level); (ii) composed in the following way:
# for a multi‑level wildcard (i.e., an arbitrary number of
• Rule’s name, which de ines a unique name to refer‑
topic levels). When a message is published under a cer‑
tain topic, it is delivered to each matching subscription ence the rule
registered at that time.
• When statement, which provides the trigger to acti‑
In the case study presented in Section 4, MQTT protocol vate the rule
plays a central role in message passing, due to its ef i‑
• Then statement, which de ines the tasks to be per‑
ciency for the investigated scenario.
formed when the rule is triggered.
3.2 InluxDBԀ 3.4 Ignition

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InluxDBԀ is a database belonging to the NoSQL family. It Ignition 9 is a commercial, server‑based cross‑platform
has been speci ically designed and developed for manag‑ software, which is managed through web technology.
ing time‑series data, thus making it an ideal choice for pe‑ Built with customization in mind, it supports a modu‑
riodically logging sensor information. Data is stored into lar structure so that its deployment can be tailored for
”measurements” by using timestamps, ields and tags. every speci ic use case. Ignition includes a Human Ma‑
Fields are used to store data information, which can be chine Interface / Supervisory Control And Data Acquisi‑
strings, loats, integer or boolean and are always associ‑ tion (HMI/SCADA), which can be built, in a customized
ated with a timestamp. Tags are similar to ields, but are way, depending on the intended purpose. Ignition makes
also indexed; this allows the storage of important meta‑ use of tags as points of data; these can be both static or
data in tags to optimize querying performance. InluxDBԀ dynamic on the basis of the inal scope. While it provides
is adopted in the case study, presented in Section 4, since a set of prede ined types, it also allows the user to extend
its data structure perfectly its the need of heterogeneity, them through the use of User Data Types (UDT tags). The
which is dictated by IoT environments. basic tags are the following:
• OPC Tags are particular kinds of tag, which use the
Open Process Connectivity (OPC) standard to com‑
municate and read/write values directly to the Pro‑
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MQTT v3.1/v3.1.1, https://mqtt.org/mqtt‑speci ication/ grammable Logic Controller (PLC).
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source v3.1/v3.1.1 broker.
http://mosquitto.org 8 Openhab, open source automation software. https://www.openhab.org
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HiveMQ MQTT broker. https://www.hivemq.com Ignition software. https://inductiveautomation.com
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In luxDB, time series platform. https://www.in luxdata.com/

© International Telecommunication Union, 2021 31