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... see [[https://en.wikipedia.org/wiki/MQTT|Wikipedia]] | ... see [[https://en.wikipedia.org/wiki/MQTT|Wikipedia]] | ||
+ | ... see [[https://www.hivemq.com/blog/mqtt-essentials-part-1-introducing-mqtt]] | ||
+ | |||
+ | ... see [[https://blog.doubleslash.de/mqtt-fuer-dummies/]] | ||
===== MQTT Data Flow by Examples ===== | ===== MQTT Data Flow by Examples ===== | ||
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{{ :tut:mqtt:mqtt1.svg?600x0 }} | {{ :tut:mqtt:mqtt1.svg?600x0 }} | ||
- | If Client X publishes any data with Topic 1 and nobody is listening (nobody has subscribed Topic 1) the data is lost. | + | If Client X publishes any data with Topic 1 and nobody is listening (nobody has subscriped Topic 1) the data is lost. |
(Exception: see Topics with Retain Flag) | (Exception: see Topics with Retain Flag) | ||
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* Client A connected | * Client A connected | ||
- | * Client B connected and subscribes Topic 2 | + | * Client B connected and subscripes Topic 2 |
{{ :tut:mqtt:mqtt2.svg?600x0 |}} | {{ :tut:mqtt:mqtt2.svg?600x0 |}} | ||
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* Client A, C, E connected | * Client A, C, E connected | ||
- | * Client B connected and subscribes Topic 2 | + | * Client B connected and subscripes Topic 2 |
- | * Client F connected and subscribes Topic 3 | + | * Client F connected and subscripes Topic 3 |
{{ :tut:mqtt:mqtt3.svg?600x0 }} | {{ :tut:mqtt:mqtt3.svg?600x0 }} | ||
- | Any Client can publish any data with any Topic at anytime. The subscriping Clients are notified instantly about change of the Topics they subscripes and only that. | + | Any Client can publish any data with any Topic at anytime. The subscribing Clients are notified instantly about change of the Topics they subscripes and only that. |
==== Example: Many Publisher, 1 Subscriber with Wildcard ==== | ==== Example: Many Publisher, 1 Subscriber with Wildcard ==== | ||
* Client A, C, E connected | * Client A, C, E connected | ||
- | * Client D connected and subscribes Topic with '#' | + | * Client D connected and subscripes Topic with '#' |
{{ :tut:mqtt:mqtt4.svg?600x0 }} | {{ :tut:mqtt:mqtt4.svg?600x0 }} | ||
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==== Example: Request and Answer ==== | ==== Example: Request and Answer ==== | ||
- | * Client E connected and subscribes Topic 4 | + | * Client E connected and subscripes Topic 4 |
- | * Client F connected and subscribes Topic 3 | + | * Client F connected and subscripes Topic 3 |
{{ :tut:mqtt:mqtt5.svg?600x0 }} | {{ :tut:mqtt:mqtt5.svg?600x0 }} | ||
- | Every Client can be publisher and subscriper. For sneding a request/command one Topic can be used. For the answer an other Topic is used. | + | Every Client can be publisher and subscriber. For sneding a request/command one Topic can be used. For the answer an other Topic is used. |
Note: This can be solved with only one Tpoic but the publisher would receive his own request/command. | Note: This can be solved with only one Tpoic but the publisher would receive his own request/command. | ||
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* Client G connected | * Client G connected | ||
- | * Client H connected and subscribes Topic 5 with QoS | + | * Client H connected and subscripes Topic 5 with QoS |
{{ :tut:mqtt:mqtt6.svg?600x0 }} | {{ :tut:mqtt:mqtt6.svg?600x0 }} | ||
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|2|garantee that data arrives only once| | |2|garantee that data arrives only once| | ||
- | Note: Each publisher and each subscriper can user the QoS flag without affecting the others. | + | Note: Each publisher and each subscriber can user the QoS flag without affecting the others. |
==== Example: Remain-Flag ==== | ==== Example: Remain-Flag ==== | ||
* Client Y was connected long time ago | * Client Y was connected long time ago | ||
- | * Client Z connects now and subscribes Topic 6 | + | * Client Z connects now and subscripes Topic 6 |
{{ :tut:mqtt:mqtt7.svg?600x0 }} | {{ :tut:mqtt:mqtt7.svg?600x0 }} | ||
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|0|fire and forget| | |0|fire and forget| | ||
|1|saved on broker| | |1|saved on broker| | ||
+ | |||
+ | ===== Topic Wording ===== | ||
+ | |||
+ | There is no law that you have to name your topics in a special way. So the following names are (principle) correct: | ||
+ | |||
+ | * /MyHome/Kitchen/Temperature | ||
+ | * /MYHOME/KITCHEN/TEMPERATURE | ||
+ | * MyHome/Kitchen/Temperature | ||
+ | * MyHome.Kitchen.Temperature | ||
+ | * MyHomeKitchenTemperature | ||
+ | * MHKT | ||
+ | * /Temperature/Kitchen/MyHome | ||
+ | * 42 | ||
+ | |||
+ | But there are some guidelines for names that all clinets can filter and handle subscriptions in an easy way: | ||
+ | |||
+ | * The topic begins with a '/' | ||
+ | * The topic do NOT end with a '/' | ||
+ | * A '/' seperates topic levels | ||
+ | * The topic levels starts with the most commen level | ||
+ | |||
+ | So the recommented name is: | ||
+ | |||
+ | * /MyHome/Kitchen/Temperature | ||
+ | |||
+ | ===== Subscription Wildcard Examples ===== | ||
+ | |||
+ | ==== Exact Match ==== | ||
+ | |||
+ | On subscribing **"/MyHome/Kitchen/Temperature"** you get: | ||
+ | * **/MyHome/Kitchen/Temperature** | ||
+ | * <del>/MyHome/Kitchen/Humity</del> | ||
+ | * <del>/MyHome/Kitchen/Fridge/Temperature</del> | ||
+ | * <del>/MyHome/Livingroom/Temperature</del> | ||
+ | * <del>/MyHome/Livingroom/Humity</del> | ||
+ | * <del>/MyGarden/Air/Temperature</del> | ||
+ | * <del>/MyGarden/Pool/Temperature</del> | ||
+ | |||
+ | ==== # Wildcard ==== | ||
+ | |||
+ | On subscribing **"/#"** you get: | ||
+ | * /MyHome/Kitchen/Temperature | ||
+ | * /MyHome/Kitchen/Humity | ||
+ | * /MyHome/Kitchen/Fridge/Temperature | ||
+ | * /MyHome/Livingroom/Temperature | ||
+ | * /MyHome/Livingroom/Humity | ||
+ | * /MyGarden/Air/Temperature | ||
+ | * /MyGarden/Pool/Temperature | ||
+ | |||
+ | On subscribing **"/MyHome/#"** you get: | ||
+ | * **/MyHome/**Kitchen/Temperature | ||
+ | * **/MyHome/**Kitchen/Humity | ||
+ | * **/MyHome/**Kitchen/Fridge/Temperature | ||
+ | * **/MyHome/**Livingroom/Temperature | ||
+ | * **/MyHome/**Livingroom/Humity | ||
+ | * <del>/MyGarden/Air/Temperature</del> | ||
+ | * <del>/MyGarden/Pool/Temperature</del> | ||
+ | |||
+ | On subscribing **"/MyHome/Kitchen/#"** you get: | ||
+ | * **/MyHome/Kitchen/**Temperature | ||
+ | * **/MyHome/Kitchen/**Humity | ||
+ | * **/MyHome/Kitchen/**Fridge/Temperature | ||
+ | * <del>/MyHome/Livingroom/Temperature</del> | ||
+ | * <del>/MyHome/Livingroom/Humity</del> | ||
+ | * <del>/MyGarden/Air/Temperature</del> | ||
+ | * <del>/MyGarden/Pool/Temperature</del> | ||
+ | |||
+ | ==== + Wildcard ==== | ||
+ | |||
+ | On subscribing **"/MyHome/+/Temperature"** you get: | ||
+ | * **/MyHome/**Kitchen**/Temperature** | ||
+ | * <del>/MyHome/Kitchen/Humity</del> | ||
+ | * <del>/MyHome/Kitchen/Fridge/Temperature</del> | ||
+ | * **/MyHome/**Livingroom**/Temperature** | ||
+ | * <del>/MyHome/Livingroom/Humity</del> | ||
+ | * <del>/MyGarden/Air/Temperature</del> | ||
+ | * <del>/MyGarden/Pool/Temperature</del> | ||
+ | |||
+ | On subscribing **"/+/+/Temperature"** you get: | ||
+ | * /MyHome/Kitchen**/Temperature** | ||
+ | * <del>/MyHome/Kitchen/Humity</del> | ||
+ | * <del>/MyHome/Kitchen/Fridge/Temperature</del> | ||
+ | * /MyHome/Livingroom**/Temperature** | ||
+ | * <del>/MyHome/Livingroom/Humity</del> | ||
+ | * /MyGarden/Air**/Temperature** | ||
+ | * /MyGarden/Pool**/Temperature** | ||
+ | |||
+ | On subscribing **"/+/+/+/Temperature"** you get: | ||
+ | * <del>/MyHome/Kitchen/Temperature</del> | ||
+ | * <del>/MyHome/Kitchen/Humity</del> | ||
+ | * /MyHome/Kitchen/Fridge**/Temperature** | ||
+ | * <del>/MyHome/Livingroom/Temperature</del> | ||
+ | * <del>/MyHome/Livingroom/Humity</del> | ||
+ | * <del>/MyGarden/Air/Temperature</del> | ||
+ | * <del>/MyGarden/Pool/Temperature</del> | ||
+ | |||
+ | |||