MQTT, TR50 and Telit HE910

[Patrick Collins]

I am trying to understand the architecture of the Telit xE910 and the use of MQTT and TR50. The documentation while very detailed in some areas is quite weak in describing the overall architecture. What I am trying to do is use the Telit xE910 modules and their AT#DW series commands to send TR50 data to our Mosquitto MQTT broker and get the module to receive the TR50 reply. What I don't understand at this point is how do I send TR50 replies back to the xE910. I assume that the xE910 is a MQTT client that publishes message on the "api" topic but what I can't work out is what topic does the module subscribe to receive the TR50 reply.

I have asked this question on the Telit support forum but either I'm not explaining myself well enough, my question isn't understood or ?

Hope someone can help me.

Paddy

[Paul Fremantle]

Looking at the documentation it looks like you need to publish to the topic reply:

From: https://help.devicewise.com/display/M2MOpen/MQTT+Interface

• Commands are sent on topic "api", and replies are received on topic "reply".
• When you connect, you are automatically subscribed to the following topics:
  • reply/#
  • replyz/#
  • notify/#
    
    

I'd say this was a problem, as all your devices are going to get all replies, since Mosquitto and other brokers behave that way (if you publish to /reply all devices get it. To solve that, I would recommend publishing to /reply/{clientid}/ and then using Mosquitto's ACLs to only allow 

pattern read /reply/%c/ 

(see https://mosquitto.org/man/mosquitto-conf-5.html)

That should sort you out I hope.

Paul

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Paul Fremantle

Doctoral Researcher, University of Portsmouth, School of Computing

Visiting Scientist, Institute of the Architecture of Application Systems, Stuttgart

Visiting Lecturer, Software Engineering Programme, Oxford University

Co-Founder, WSO2
Apache Member and Committer

email: paul.fr...@port.ac.uk, pa...@fremantle.org

twitter: pzfreo / skype: paulfremantle / blog: http://pzf.fremantle.org

[Patrick Collins]

Paul,

Thanks very much for that. I was just about to try it when the Seagate Barracuda in one of the test servers gave up the ghost. Currently rebuilding it and should be able to test hopefully later tonight.

Cheers Mate.

Paddy

[Patrick Collins]

Paul,

I tried this but found that the xE910 doesn't subscribe to any topics and so Mosquitto doesn't send posts to it regardless of which topic I post to, e.g. reply, replyz, etc. I know this works with the Telit MQTT server so I suspect they are using something custom that is able to send messages directly to clients regardless of whether they are subscribed to a topic.

Regard.

Patrick

[Paul Fremantle]

Patrick

That is bad luck. I guess you should take it up with Telit. 

I don't have one so I can't help you more. The only thing I'd suggest is putting a Wireshark on the server network or possibly sticking an MQTT proxy in between. There is an MQTT 3.1.1 proxy here: https://github.com/eclipse/paho.mqtt.testing/blob/master/interoperability/run_proxy.py (you need the rest of the code tree as well).

Paul

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[Jeremy Turner]

Hi

Did you get the reply to work?