38
votes
Accepted
When and why to use MQTT protocol?
MQTT is a "messenger" between devices:
your device measures at time T a temperature of X degrees
it connects (itself or via the zwave hub) to the MQTT broker
it create a message with the topic /...
- 3,686
29
votes
Accepted
What is the difference between MQTT and Web Sockets, and when should I use them?
The question setting here is little bit misleading, because actually these protocols cannot at all be compared together. They are like TCP and IP, layers above each other. [1]
Websockets is a low ...
- 4,301
23
votes
When and why to use MQTT protocol?
MQ Telemetry Transport Protocol known as MQTT is designed for devices which run on low power and low bandwidth. It is a lightweight publish/subscribe messaging protocol which means any other device ...
- 1,520
20
votes
Accepted
Can an MQTT client subscribe to a topic created by itself?
Yes, it is possible to subscribe to a topic that is created by itself.
An MQTT client can be both a publisher & subscriber at the same time. In MQTT terms, a client includes both subscribers and ...
- 1,520
16
votes
Is MQTT protocol appropriate for transmitting sensor readings over BLE?
MQTT has to run over TCP/IP (I can't remember if it's actually in the spec or if just enough assumptions are made to make it so) but its sister protocol MQTT-SN can be run over nearly any protocol ...
- 12.5k
15
votes
Accepted
Can Mosquitto support multiple brokers?
Yes, Mosquitto does support multiple brokers.
Mosquitto uses MQTT Bridges to connect multiple brokers thus routing messages between these mosquitto brokers. This way a bridge between your primary ...
- 2,479
13
votes
What is the difference between MQTT and Web Sockets, and when should I use them?
They're comparable in that both allow you to have full-duplex communication such that the server can immediately pass data to the client, without the client polling for it (as might be with HTTP).
...
- 596
13
votes
Accepted
Would RPI 3 serve as IoT server with MQTT?
A Raspberry Pi 3 is a pretty serious bit of kit when you think about it
Quad core Arm Cortex
1gb of RAM
a onboard GPU
That is a huge amount of memory, easily more than enough to run a MQTT broker ...
- 12.5k
12
votes
Accepted
What simple security tests can I perform on my MQTT network?
Some ideas - I've not covered all combinations of with/without username/TLS, hopefully you can see where they are missing.
Can a client connect anonymously, no TLS?
mosquitto_sub -t test/topic -h &...
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12
votes
Accepted
Don’t subscribe to # - so how to dump all messages to database with Mosquitto?
a similar system (extension/plugin) for the mosquitto broker
As far as I know there is no plugin/extension for mosquitto broker ( at least no opensource one )
another recommended method that works ...
- 1,520
12
votes
When and why to use MQTT protocol?
MQTT (Message Queue Telemetry Transport) seems to be well suited for the proposed application.
It is lightweight both with respect to bandwidth (smallest packet size with a header of just 2 bytes) ...
- 2,479
12
votes
Accepted
How can I implement MQTT on an STM32F030K6T6?
Is it possible to implement MQTT on this device?
Any device that has TCP/IP layer can implement MQTT.
What requirements should a microcontroller match to be able to use/run MQTT?
You need to ask ...
- 1,520
12
votes
Are there any devices with open-source protocols over Wi-Fi?
The IKEA Trådfri lighting system is all CoAP based, you can find my write up on the protocol here
Belkin WeMo devices are all uPnP and SOAP controlled as well so another open/self describing protocol
- 12.5k
11
votes
Accepted
Confusion about client-server connection establishment in MQTT
Does this mean that if a Client subscribes, then it remains connected to the server while the subscription is valid even though there are no data flow in most of the time?
Yes, once the connection is ...
- 126
11
votes
Don’t subscribe to # - so how to dump all messages to database with Mosquitto?
This discussion on the openHAB mailing list seems to suggest there's no issue with using # as a subscription to receive all messages:
Whilst troubleshooting MQTT devices, it occurred to me ...
- 18.2k
11
votes
How can I implement MQTT on an STM32F030K6T6?
The mbed mmqt library doesn't seem to document any memory requirements as likely to be limiting, and can reasonably be assumed to be targetted at this sort of small-footprint device as an endpoint. ...
- 10.4k
11
votes
Accepted
What happens if Mosquitto runs out of memory to store QoS 1/2 messages?
Messages are persisted to disk not just held in memory.
Look at the autosave_interval and autosave_on_change options for when the messages get written to disk.
Source
- 12.5k
11
votes
Accepted
How can I interface a LoraWan network with MQTT?
Imagine your network as a Venn diagram where one set is LoraWan and the other is MQTT.
Elements in the sets should know only about their set(s).
So nodes using LoraWan (are in the LoraWan set) do ...
- 7,553
11
votes
Is MQTT protocol appropriate for transmitting sensor readings over BLE?
Arguably, you'd be better off doing a simple mapping of the data from BLE paradigms to MQTT, rather than trying to literally send MQTT over BLE.
BLE generally exchanges data in the form of ...
- 1,878
10
votes
Accepted
What happens when there is not any subscriber to a topic in MQTT?
As you say, it depends on the server implementation, especially the QoS of the transmitted message if it is "at least once".
IMHO MQTT is a broadcasting system, not a end-to-end protocol between two ...
- 3,686
10
votes
Don’t subscribe to # - so how to dump all messages to database with Mosquitto?
I think it is important to consider that there are many different use cases for MQTT brokers, as with any piece of software.
Handling chat messages for a billion users (many users, relatively low ...
- 830
10
votes
Accepted
mosquitto_sub "connection refused" on Arch Linux
Turns out there is no broker running on the Arch system whereas installing mosquitto on Raspbian automatically starts it. Simply enable and start the broker.
Start the systemd service.
systemctl ...
- 2,479
10
votes
Can Mosquitto support multiple brokers?
In .NET the implementation allows to connect one client to one broker, so I'd say why not...
MqttClient mqtt;
string broker = ini.getData("MQTT", "hostname");
mqtt = new MqttClient(broker);
mqtt....
- 3,686
10
votes
Are there MQTT brokers that persist QoS 1/2 messages to disk?
I think Mosquitto saves the in-memory messages to disk.
persistence [ true | false ]
If true, connection, subscription and message data will be written to the disk in mosquitto.db at the ...
- 200
10
votes
Accepted
Should I use special characters in MQTT topics?
Goufalite is entirely correct about this problem: it's not a technical issue at all, just a naming problem, so a lot of the advice is very opinionated based on the author's idea of what names are best....
- 18.2k
10
votes
Is it a bad practice to keep certificates on external memory?
A little bit of context
Since you're using MQTT with AWS IoT, you're expected to use X.509 certificates for authentication and security. Amazon have a little bit of guidance about how you should ...
- 18.2k
10
votes
Accepted
How to enable WebSockets on Mosquitto running on Windows?
A few things:
The mosquittto_pub and mosquitto_sub commands do not support WebSockets at all.
When you run mosquitto from the command line you have to explicitly point to the config file with the -c ...
- 12.5k
10
votes
Performance of MQTT over TLS vs. MQTT
I wouldn't expect the difference to be too significant, once the connection is set up.
A breakdown of the overhead that TLS produces in general can be found here. The important bits are:
The ...
- 18.2k
10
votes
Accepted
MQTT broker accessible from outside without opening port in firewall?
You basically have 3 options if you don't want to forward a port.
Use a broker in the cloud so client from home always connect out to it. Use TLS and authentication so others can't eavesdrop or ...
- 12.5k
10
votes
Accepted
Can I use an ESP8266 as an MQTT broker?
Technically speaking, yes, an ESP8266 could act as an MQTT broker. In fact, someone has already tried it! By the end of their project, they claimed to have a broker that can bridge to a cloud MQTT ...
- 18.2k
Only top scored, non community-wiki answers of a minimum length are eligible