You get 10 good-quality PCBs manufactured and shipped to your doorstep for cheap. You will also get a discount on shipping on your first order. Upload your Gerber files onto PCBWAY to get them manufactured with good quality and quick turnaround time. Check out their online Gerber viewer function. With reward points, you can get free stuff from their gift shop.

• Client: An MQTT client is any device from a microcontroller up to a fully-fledged server that runs an MQTT library and connects to an MQTT broker over a network. A Client can be either a publisher(The one who is sending the message) or a subscriber(The one who is receiving the message). Basically, the devices which are connected to the MQTT Broker are considered Clients. If a client is acting as a publisher then it will send its message to the broker. The broker will filter the received message based on topics. If a client is acting as a subscriber, then it will subscribe to the topic from which it needs the message and the broker will give it access to the messages stored on that topic.
• Broker: An MQTT broker is a server that receives all messages from the clients and then routes the messages to the appropriate destination clients. A broker also filters the messages on the basis of topics and helps clients get access to their required messages easily and quickly.
• Topic: In MQTT, the word topic refers to a UTF-8 string that the broker uses to filter messages for each connected client. The topic consists of one or more topic levels. Each topic level is separated by a forward slash. In comparison to a message queue, MQTT topics are very lightweight. The client does not need to create the desired topic before they publish or subscribe to it. The broker accepts each valid topic without any prior initialization.

MQTT works on a publish/subscribe pattern which provides an alternative to the traditional client-server architecture. In a client-server model, the client communicates directly to the endpoint but this is not the case in the pub/sub-model. Here the communication is settled through an MQTT broker which acts as a middle man for the communication and takes the message from one end to the other. Every message is a discrete chunk of data, opaque to the broker. Every message is published to an address on the broker, known as a topic. Clients may subscribe to multiple topics. Every client subscribed to a topic receives every message published to the topic. The decoupling between subscriber and publisher has three dimensions which are:-

• Space decoupling, which means that the publisher and subscriber do not exchange any IP address and port.
• Time decoupling, in which Publisher and Subscriber do not run at the same time.
• Synchronization decoupling, in which operations on both sides are not needed to be interrupted during publishing or subscribing.

MQTT is a command-response protocol that's why each command is acknowledged whether it is the Command to establish a connection or a command to publish or subscribe. It uses TCP/IP protocol to connect to the broker. As the TCP/IP protocol is connection-oriented and has error correction capability it ensures that the packets are received in order and the information transfer is reliable.

• Authentication: MQTT provides authentication of every user who intends to publish or subscribe to particular data. The user id and password are stored in the API database. While connecting to the MQTT broker, we provide the username name and password, and the MQTT Broker will validate the credentials based on the values present in the database.
• Access Control: MQTT determines which user is allowed to access which topics. By default, all users are allowed to access all topics.
• QoS: The Quality of Service (QoS) level is the Quality transfer of messages which ensures the delivery of messages between sending body & receiving body. There are 3 QoS levels in MQTT:-

1) At most once(0) –The message is delivered at most once, or it is not delivered at all.

2) At least once(1) – The message is always delivered at least once.

3) Exactly once(2) – The message is always delivered exactly once.

• Distribute information more efficiently
• Increase scalability
• Reduce network bandwidth consumption dramatically
• Reduce update rates to seconds
• Very well-suited for remote sensing and control
• Maximize available bandwidth
• Extremely lightweight overhead
• Very secure with permission-based security
• Used by the oil-and-gas industry, Amazon, Facebook, and other major businesses
• Saves development time
• Publish/subscribe protocol collects more data with less bandwidth compared to polling protocols

Some of the drawbacks of MQTT are:-

• Slower transmit cycle. Fast cycles are critical for systems with more than 250 devices.
• Lack of security encryption. While MQTT uses Transport Layer Security/Secure Sockets Layer (TLS/SSL), it is primarily unencrypted.
• Scalability. Creating a globally scalable network is more difficult with an MQTT protocol compared to other competitors

• Built on a stable AWS service
• Use MQTT protocol suitable for low-data-volume and power-saving mode
• Devices that support the MQTT protocol can be used.
• Compatibility testing of all mainstream IoT communication modules is completed
• Support Android, iOS, Windows, Linux
• Low-cost access to the cloud platform
• Use simple instructions to quickly integrate the IoT cloud platform

To get some more details about the Reyax RYC1001 MQTT Broker you can check the datasheet of the product from here

So this brings us to the end of this tutorial. In the next part of this tutorial we are going to get our hands on the MQTT technology and by applying that we will make a relay board that will have an ESP8266 as well and will be capable of connecting to the internet. It will basically act as a smart plug which we would be able to control from any place where the Internet is available. The board that we will make will be MQTT-based and you will enjoy making it. So check out the next tutorial if you want to get yourself started with MQTT.