MQTT is a machine-to-machine (M2M) and
Internet of Things (IoT) open protocol standardized by the OASIS Technical Committee (www.oasis-open.org). The protocol is easy
to adopt for a wide variety of IoT devices, platforms, and operating systems. Enterprise cloud platforms such as Microsoft
Azure expose their IoT PaaS through MQTT.
This blog post covers the core concepts of MQTT that are necessary for building M2M and IoT applications. It covers the basic terminology, along with a section on integrating MQTT with an IoTView HMI.
MQTT was created in 1999 by Andy Stanford-Clark and Arlen Nipper. The motivation for designing MQTT was to create a lightweight and bandwidth-efficient protocol that was data agnostic with support for multiple levels of Quality of Service. Today, those are the same reasons for which MQTT is chosen for implementing IoT solutions.
How
does MQTT Work?
MQTT was designed as an extremely lightweight
Publish/Subscribe messaging
transport. It is useful for connections with remote locations where a small code footprint is required and/or
network bandwidth is at a premium.
MQTT uses the publisher & subscriber
pattern to connect interested parties with each other. It does it by decoupling
the sender-publisher with the receiver -subscriber. The publisher sends a
message to a central topic which has multiple subscribers waiting to receive
the message. The publishers and subscribers are autonomous, which means that
they do not need to know the presence of each other.
Where can it be used?
The
MQTT has been used in sensors communicating
to a Broker via satellite link, over occasional dial-up connections, and
in a range of automation and small device scenarios. It is also ideal for mobile applications because of
its small size, low power usage, minimized data packets, and efficient
distribution of information to one or many receivers
Terminology:Client, Broker, Topic, Quality of Service
Client – Any
publisher or subscriber that connects to the centralized broker over a network
is considered to be the client. It’s important to note that there are servers
and clients in MQTT. Both publishers and subscribers are called as clients
since they connect to the centralized service. Clients can be persistent or
transient. Persistent clients maintain a session with the broker while
transient clients are not tracked by the broker. Clients often connect to the
broker through libraries (Sample libraries available for C, C++, Go, Java, C#,
PHP, Python, Node.js, and Arduino) and software development toolkits (SDKs).
Examples of clients (or sometime refers to as a publisher):Sensors, PLCs, or just about any device creating data
Examples of clients (or sometime refers to as a publisher):Sensors, PLCs, or just about any device creating data
Broker: The Broker is primarily responsible for:
·
receiving all messages and
·
filtering them
·
deciding who is interested
·
sending the message to all subscribed
clients
·
the authentication and authorization
of clients
It also holds the session of all persisted
clients including subscriptions and missed messages.
The broker is the central hub, which every
message needs to pass
Topic:
A Topic In MQTT is a hierarchical structured
string, which is used for message filtering and routing and determines which
message gets to which client. It acts as the central distribution hub for
publishing and subscribing messages.
Connection – MQTT
can be utilized by clients based on TCP/IP. The standard port exposed by
brokers is 1883, which is not a secure port. Those brokers who support TLS/SSL
typically use port 8883. For secure communication, the clients and the broker
rely on digital certificates.
Quality of Service
This
value determines how the client and the server communicate to deliver
the message.
Hands-on
with MQTT
Now that the key concepts were covered, let’s
see MQTT in action. This section will help you understand the essence of MQTT. IoT
View Runtime of InTouch Machine Edition is used to illustrtae
Installing the broker
One open source software MQTT broker is called
Mosquitto. For installation instructions, please
refer to the installation guide.
Architectures
Sample Applications Goals
- Distributed Data Acquisition, Manipulation and Control
- Centralized Management
- Scalable – Large number of devices
- Secure – Encryption, Filtering, Remote notification
- Platform agnostic – Both local runtime and remote Thin Clients
- Simple - Easy to configure, deploy, and maintain
- CONNECT: Broadening the connectivity layer with low-cost, low-power sensors (Ex: IoTView)
- COLLECT: Storing massive amounts of industrial data on premise and in the Cloud (Ex: Wonderware Online)
- CONTEXTUALIZE: Converting industrial data to meaningful analytics (Ex: Prism)
- CLOSE THE LOOP: Delivering real-time actionable information and business logic (Ex: Smart Glance)
InTouch Machine Edition is an easy to use development and runtime (ex:
IoTView) software that is designed for the embedded operating systems. It has strong integration with the Wonderware
portfolio of products such as System Platform and Wonderware Online. It is the perfect solution for embedded HMI
on the plant floor, IIoT or IoT / Industry 4.0 solutions.
How is the InTouch Machine Edition & IoTView
used?
- Design an application once and deploy it to any embedded device that supports Windows Embedded, Linux and VxWork.
- Remote visualization using web browsers or viewers
- Full RT – Windows PC Runtime
- Embedded Standard – Runtime for Windows Embedded Standard
- IoTView – Platform Agnostic Runtime (Linux)
MQTT seems to be the preferred protocol for M2M and IoT applications. Based on the publisher & subscriber pattern, it simplifies the connectivity between devices. This post attempted to introduce you to the basics of MQTT. I will cover other aspects of MQTT including cyber security and practical applications in the upcoming posts.
References:
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