myServer6 now supports MQTT technology.

Introduction

In this tutorial, you'll learn everything you need to know about the MQTT messaging protocol, why you would want to use it, and how it's implemented. In a nutshell, MQTT uses your existing Internet home network to send messages to your IoT devices and respond to those messages.

Brief History

MQTT (Message Queuing Telemetry Transport) is a publish/subscribe messaging protocol that works on top of the TCP/IP protocol. The first version of the protocol was developed by Andy Stanford-Clark of IBM and Arlen Nipper of Cirrus Link in 1999. What makes MQTT faster than say sending HTTP requests with your IoT device is MQTT messages can be as small as 2 bytes, whereas HTTP requires headers which contains a lot of information that other devices might not care about. Also, if you have multiple devices waiting for a request with HTTP, you'll need to send a POST action to each client. With MQTT, when a server receives information from one client, it will automatically distribute that information to each of the interested clients.

The protocol uses a publish/subscribe architecture in contrast to HTTP with its request/response paradigm. Publish/Subscribe is event-driven and enables messages to be pushed to clients. The central communication point is the MQTT broker, it is in charge of dispatching all messages between the senders and the rightful receivers. Each client that publishes a message to the broker, includes a topic into the message. The topic is the routing information for the broker. Each client that wants to receive messages subscribes to a certain topic and the broker delivers all messages with the matching topic to the client. Therefore the clients don’t have to know each other, they only communicate over the topic. This architecture enables highly scalable solutions without dependencies between the data producers and the data consumers.

MQTT Publish/Subscribe Architecture

The difference to HTTP is that a client doesn’t have to pull the information it needs, but the broker pushes the information to the client, in the case there is something new. Therefore each MQTT client has a permanently open TCP connection to the broker. If this connection is interrupted by any circumstances, the MQTT broker can buffer all messages and send them to the client when it is back online. As mentioned before the central concept in MQTT to dispatch messages are topics. A topic is a simple string that can have more hierarchy levels, which are separated by a slash. A sample topic for sending temperature data of the living room could be house/living-room/temperature. On one hand the client can subscribe to the exact topic or on the other hand use a wildcard. The subscription to house/+/temperature would result in all message send to the previously mention topic house/living-room/temperature as well as any topic with an arbitrary value in the place of living room, for example house/kitchen/temperature. The plus sign is a single level wild card and only allows arbitrary values for one hierarchy. If you need to subscribe to more than one level, for example to the entire subtree, there is also a multilevel wildcard (#). It allows to subscribe to all underlying hierarchy levels. For example house/# is subscribing to all topics beginning with house.

Use Case 1

In order to make the subsequent code more understandable, we will use the transferring of sensor data from a temperature and brightness sensor to a control center over the internet as an example. The sensors will be connected to a Raspberry Pi, which acts as gateway to the MQTT broker, which can reside in the cloud, or us myServer6. On the other side is a second device, the control center, that also has an MQTT client and receives the data. Additionally we will implement a notification, which alerts the control center if the sensor is disconnected.

Communication between the sensor client and the control center (myServer6) over MQTT

Use Case 2

For this example, we will connect Homeseer home automation application with myServer6.  Homeseer has it's roots like Allonis and has a passionate customer base that includes 3rd party developers.  These developers have created many interesting projects.  myServer6 has a more capable user interface and media content and device support.  So, let's connect them to get the best out of both products!

Michael McSharry is a prolific developer for the Homeseer platform.  He has created the "mcsMQTT" plugin.  This is a very capable and well documented MQTT addon.  We will use that to connect to myServer's built in MQTT capability.