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MQTT - An overview


Disclaimer

All the following information is not guaranteed. I try to research all information correctly and to summarize, but in the end I am only a person who, in his Makes leisure and wants to learn something

– If I made a mistake or just wrong have published information, then write a comment! – I will read this and if I can verify the information, my text with a hint of your comment ^

This blog is for everyone and should help anyone who learns something . That is why I also ask for a friendly one

Introduction

Within the last few years I have the MQTT protocol for many my projects used. MQTT is very easy to use, relying on usually existing TCP networks, offers security functions and is a pure M2M (machine to machine) protocol.
MQTT running until then always in some form in my smarthome and has me, different from ZigBee, for example, never abandoned.
In short is MQTT, in my opinion, one of the best protocols to be found in can use home automation. The question is here – why then almost nobody does it?

This contribution (and some more) will be accompanied by this question and continue to focus on the possibilities of MQTT in.

SPOILER: MQTT can do a lot, is one of the oldest M2M protocols (introduced in 1999) and has far not come out of fashion.

MQTT is a very large protocol, with many possibilities and Drop knitting. I will therefore always divide the posts and link to each other. Please bear in mind that I have this in my free time, so I won't get rhythm in the perfect weeks can post, but I will try a certain continuity to hold.

If you want to read the current specification, you can read this here find.

Main part

What is MQTT and how does it work?

Here we start again from the very front. MQTT is like mentions an M2M (machine to machine) protocol, but what does that mean? – Machine to machine communication only describes that the Communication between two (or more) machines takes place.
Each MQTT infrastructure consists of (one) broker and clients. Each client subscribes to special topics that contain or receive information can (more so later) Send clients (publish) and receive Information about the broker.

Publish / Subscribe – What is this?

MQTT implements the so-called Publish and Subscribe Pattern. Here become information through a “publish”, in a defined topic by the broker “published”. Each of the Information (or basically the topic) Interested, this can be Subscribe to topic (Subscribe) and receive the message by the MQTT Broker ( offline devices can also do this message later received. More in one of the following posts).

The use of this infrastructure is as simple as ingenious. Each device can basically open any topic. It is necessary to only a few formal requirements are complied with. A topic can be found Example that fold: “home/home room/temperature” – this Topic could be used for example to get the current temperature in to provide living room.
A thermometer would be in this case post the topic (Publish). This information will be processed (and possibly held). All clients at the temperature the living room are “interessed”, for example the heating control of living room, can subscribe to the topic (Subscribe) and get always the current temperature in the living room. Here is to mention that can send multiple devices to a topic and multiple devices to a topic can subscribe. The node always forms the broker. This forms an advantage: Clients do not have to know each other or be on the same network. Any client who sends or receive wants to achieve only the MQTT broker. The rest is the broker.

Are there alternatives?

There are still so-called filter queries. These can be Content Based, depending on the content or types sent be. In these two types of communication, however, I will not or only on the edge, since these in Smarthome environments are rare and no one knows me at least in the private environment that uses this type of MQTT communication.

MQTT Secure – Is that possible?

Depending on which data run via the broker, these should be (e.g. by encryption). This is also with MQTT easily possible.
MQTT generally supports some Security functions. Since MQTT works on L8, it is also underlying technique used.
The layers underneath already provide security mechanisms which are very widely used (e.g. TLS).
MQTT has the main purpose to be very fast and reliable. Accordingly, the standard only defines what is required. In addition, almost everything is about logic on the broker, so that basically every Device can use an MQTT client.
MQTT offers from home no transport encryption. This can be achieved by TLS on L5 ,. Furthermore, TLS gives the possibility of clients by certificate to authenticate to the server.
For example, lower security functions for inter-LAN communication form protocols such as IPSec.
MQTT offers even an L8 Payload encryption, which the sent Data encrypted. In addition, MQTT allows a user/password Authentication. Furthermore X.509.
Last post there is the possibility to assign permissions, so for example only certain devices may subscribe to a topic.
MQTT Security is also a very big topic and is later treated with more deep:).

What can I use MQTT for?

MQTT is good at transmitting small messages. The focus is at low latency. For this reason, MQTT can use all data transport within a smart home that regularly sends but not much memory required (for example sensor values a thermometer, car, rain sensor or other). I use MQTT to Example by every second mean current consumption to my Homeassistant to send.
Apart from this, applications such as security are also possible, for example, to open doors or the like.
However, data such as videos can not be transmitted via MQTT... However, this is not the purpose of the protocol.

What will come now?

This article is intended as short as possible all important information bundle. Accordingly, this contribution has been very superficial without special depth, but shows the most important. Topics like Sessions and QoS (Quality of Service) for example, I only mentioned by the way.
The the following articles will each be an aspect of the MQTT protocol treatment. In the end, I would like to have a series of blogs for the current MQTT 5 standard forms a solid gateway, with all relevant information. I would like you to put technical depth on hand, so you can put your own Build and use network.
In addition to examples from my network, I will introduce some software that can be used free of charge.

Conclusion

This post may not even apply to the extent of the MQTT Report and should not. But I think you now have a basic idea about the protocol and what it can do.
In the next item, I will focus on different aspects of this Enter Minutes to show how great MQTT for a Smarthome can be used. However, I will also show disadvantages which have no other means of communication, because MQTT has its own Disadvantages (for example the broker himself).
Nevertheless, you know and understand this protocol when you are on the move in the Smarthome area.

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