# Mqtt transmission and QoS

**URL:** <https://forum.inductiveautomation.com/t/mqtt-transmission-and-qos/63634>\
**Category:** Ignition\
**Created:** [August 31, 2022, 8:15am UTC](https://forum.inductiveautomation.com/t/mqtt-transmission-and-qos/63634 "2022-08-31T08:15:57Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Matthijs\_Maus](https://avatars.discourse-cdn.com/v4/letter/m/ecb155/32.png) [@Matthijs\_Maus](https://forum.inductiveautomation.com/u/Matthijs_Maus)\
**Post date:** [August 31, 2022, 8:15am UTC](https://forum.inductiveautomation.com/t/mqtt-transmission-and-qos/63634/1 "2022-08-31T08:15:57Z")

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Hi!  
I am testing the mqtt transmission module. I want to understand how this module publishes a topic on the broker.  
mqtt specifics define three level of QoS:

```
At most once (0)
At least once (1)
Exactly once (2)

```

What qos is used in mqtt transmission module? Is it possible to change?

Thanks

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<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [August 31, 2022, 12:16pm UTC](https://forum.inductiveautomation.com/t/mqtt-transmission-and-qos/63634/2 "2022-08-31T12:16:01Z")

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Consider posting this on Cirrus Link’s [own forum](https://forum.cirrus-link.com/). It is their module, after all.

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**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [August 31, 2022, 1:53pm UTC](https://forum.inductiveautomation.com/t/mqtt-transmission-and-qos/63634/3 "2022-08-31T13:53:48Z")

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If you’re using Sparkplug and not just a generic namespace then the QoS for various messages is defined by the spec and cannot be changed. Most messages require QoS 0, the “Birth Certificate Topic (STATE)” and “Death Certificate Topic (STATE)” require QoS 1.

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**Author:** ![kcollins](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kcollins/32/19646_2.png) [@kcollins](https://forum.inductiveautomation.com/u/kcollins)\
**Post date:** [August 31, 2022, 2:12pm UTC](https://forum.inductiveautomation.com/t/mqtt-transmission-and-qos/63634/4 "2022-08-31T14:12:30Z")

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Lots of good info here: [Eclipse Tahu | projects.eclipse.org](https://projects.eclipse.org/projects/iot.tahu)

I highly recommend reading through [the Sparkplug specification](https://projects.eclipse.org/projects/iot.tahu/downloads). Great airplane read 😃

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<div class="post-metadata">

**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [August 31, 2022, 2:20pm UTC](https://forum.inductiveautomation.com/t/mqtt-transmission-and-qos/63634/5 "2022-08-31T14:20:28Z")

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> [@kcollins](#):
>
> Great airplane read 😃

If you need a nap on an international flight, maybe 😛

These are easier to read and more up to date than the published PDFs: [sparkplug/specification/src/main/asciidoc/chapters at master · eclipse-sparkplug/sparkplug · GitHub](https://github.com/eclipse/sparkplug/tree/master/specification/src/main/asciidoc/chapters)

There might even be a way to build those into something.

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<div class="post-metadata">

**Author:** ![Matthijs\_Maus](https://avatars.discourse-cdn.com/v4/letter/m/ecb155/32.png) [@Matthijs\_Maus](https://forum.inductiveautomation.com/u/Matthijs_Maus)\
**Post date:** [September 1, 2022, 2:46pm UTC](https://forum.inductiveautomation.com/t/mqtt-transmission-and-qos/63634/6 "2022-09-01T14:46:43Z")

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Thx for the responses, eventually we used the primary host ID to buffer data, based on the QOS principle: [Primary Host ID Setting: Implementing MQTT in Ignition: Video 10 - Cirrus Link](https://cirrus-link.com/videos/primary-host-id-setting-implementing-mqtt-in-ignition-video-10/)