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Introduction
IoT stands for Internet of Things, which is a network of physical objects embedded with different types of technology that allows them to exchange information. IoT and machine-2-machine technologies need a messaging and connectivity protocol to exchange information. Protocols are used in order to provide a medium and a set of rules while exchanging information, some of the desired features of a protocol are low latency, low power consumption, small code footprint, and use of a publish/subscribe pattern. MQTT is one such protocol that fulfills all these requirements and has the momentum of big public clouds behind it.
What is MQTT?
MQTT stands for Message Queuing Telemetry Transport, it is a machine-to-machine Internet of Things connectivity protocol. Its first version was developed in 1999 by the IBM and Eurotech developers. It was initially designed to link sensors on oil pipelines and communication satellites. Later on, with version 3.1.1, it was accepted as an ISO standard.
MQTT is extremely lightweight and uses a publish-subscribe pattern. It is ideal for connecting with remote devices having a small code footprint and minimal network bandwidth. It makes it easy to communicate between multiple devices as it uses a publish/subscribe system where we can publish and subscribe to messages as clients.
Why is it used in IoT?
IoT is a network of devices that communicate with each other. Any type of communication requires some kind of protocol, to them a medium, and some set of rules for the communication. MQTT being a lightweight protocol with a fast response time, fits well into this. Whatever may be the number of devices, it makes the interaction between them efficient. One of the key features of the MQTT protocol architecture is the minimum overhead, which ensures smooth data transfer with low bandwidth. It is a good choice for a small-sized device with low power consumption.
MQTT protocol allows the transfer of data even with an unstable connection. It has three options for QoS, which is responsible for message delivery. The three options are:
QoS 0 (set as default): This is used when the information to be transmitted is not critical. In this, a publisher sends a message without requesting a guaranteed delivery. This is used when there is a stable connection.
QoS 1: This is used when the information to be transmitted is critical. In this, a publisher sends a message until it receives a delivery confirmation. QoS 1 guarantees that the subscriber receives the message. This is used when the connection is not stable.
QoS 2: This is used when the information to be transmitted is critical. In this, a publisher sends a message only once with guaranteed delivery. QoS 2 guarantees that the subscriber receives the message only once without its duplicates and overhead. This is used when the connection is not stable.
MQTT is an open protocol with a set of ready-made libraries (for C/C++, Java, Python, etc.). These open sources MQTT libraries and public brokers minimize the development costs and speed up the development process making the implementation of the MQTT protocol easy and possible in any environment.
MQTT protocol security relies on the TLS/SSL cryptographic protocols, because of which the MQTT is not among the best protocols in terms of security. Tho, additional features or security mechanisms can be added on different levels to make MQTT well secured and protected like we can use a firewall for the broker security on the network level, or we can use an encryption algorithm to make MQTT secure on the application level. By implementing end-to-end encryption, confidential messaging between clients can be enabled. One can also use access tokens to establish the client's identity to prevent unauthorized access.
To improve authentication, we need to modify the protocol and, therefore, the broker. As an off-the-shelf broker does not allow such types of modifications, we need to deploy our own broker and customize it.
Features
It operates in real-time, that is, with no delays outside of QoS.
In order to run the MQTT protocol on a device, only a few lines of code are needed.
It is very energy-efficient and very useful if a device is battery-powered or with a little CPU power.
It has ready-made libraries for various programming languages such as C/C++, Java, etc., which makes implementing the MQTT protocol very easy.
Each topic can have one retained message that a client automatically receives when it subscribes to it.
If a client unexpectedly disconnects, we can set a message instruction to be sent to all the subscribers to remedy the situation.
Architecture
There are four main components of the MQTT architecture, which are as follows:
Message: The data that is to be transferred across the network using the protocol is known as a message. When the message is transmitted over the network, it contains payload data, QoS, collection of properties, and topic name.
Client: Any device that uses MQTT is referred to as a client. In MQTT, a client has two roles- subscriber and publisher. When a client sends data to the server, it is known as a publisher, and the operation is known as publish, whereas when a client receives data from the server, it is known as a subscriber, and the operation is known as a subscription.
Server: A device that allows the client to publish/subscribe to messages is known as a server. A server accepts the network connection from the client. It then accepts the messages from the clients and then processes the subscribe and unsubscribe requests. It is also responsible for closing the network connection from the client.
Topic: It is referred to as the label provided to the message, which is checked against the subscription.
All the connected devices in the MQTT protocol are known as clients. Clients communicate with a server which is known as a broker. The broker is responsible for data transfer between the clients. Whenever a publisher (‘client’ acting as a publisher ) wants to distribute information, it publishes that information to a particular topic. Once the information is published onto the topic, the broker then sends this information to those clients that have subscribed to that topic (known as subscribers ). The publisher does not require any data or information regarding the number or location of the subscribers, and similarly, the subscribers, too, does not require any data or information about the publisher. A client can behave like a publisher or a subscriber, or both. Clients are usually not aware of each other, they only know about the broker that serves as an intermediary. This setup is popularly known as the “pub/sub model.”
Application
IBM Watson IoT platform uses MQTT as its main communication protocol.
AWS or Amazon Web Services uses MQTT as a basis for AWS IoT services. AWS IoT core uses MQTT based message broker and supports two levels of MQTT QoS.
McAfee, Red Hat, Cisco, and IECC uses MQTT for various tasks.
Microsoft Azure offers the Azure IoT hub service to build IoT applications using the MQTT protocol.
Frequently Asked Questions
From which version onwards was MQTT accepted as an ISO standard?
From version 3.1.1 and onwards, MQTT was accepted as an ISO standard.
Can a client in MQTT architecture be a publisher and subscriber?
Yes, a client in MQTT architecture can be a publisher and subscriber.
Name the pattern/mechanism that MQTT uses for exchanging information.
MQTT uses a publish-subscribe pattern/mechanism for exchanging information.
In this article, we have extensively discussed the MQTT protocol: definition, why it is used, features, architecture, and application.
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