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MQTT Protocol

  • Classification: Fundamental Training > Protocols
  • Nodes: A8-M3 x 3
  • Difficulty: High

Overview

MQTT (MQ Telemetry Transport) is a machine-to-machine (M2M) IoT connectivity protocol that was designed as an extremely lightweight publish/subscribe protocol to transport messages between devices.

In this exercise you will learn about the MQTT protocol and its constrained variant, called MQTT-SN, using RIOT OS on three A8-M3 nodes in FIT/IoT-LAB. MQTT messages published to the test/riot topic from the Saclay SSH frontend host will be displayed by the MQTT-SN client running on a RIOT OS node. The experiment nodes will have the following functions:

  • The first node will be used as a border router for propagating an IPv6 prefix through its wireless interface.
  • The second node will be used as an MQTT broker using the mosquitto.rsmb application.
  • The third node will run an MQTT-SN client to connect with the broker.

Tutorial

  1. Connect to the SSH frontend of the Saclay site of FIT/IoT-LAB by using the username you created when you registered with the testbed:

    your_computer:~$ ssh <username>@saclay.iot-lab.info

  2. Authenticate with the testbed and submit a 60 minute experiment using three A8-M3 type nodes (node firmware will be uploaded later), then wait for the experiment to start:

    username@saclay:~$ iotlab-auth -u <username>
username@saclay:~$ iotlab-experiment submit -n riot_mqtt -d 60 -l 3,archi=a8:at86rf231+site=saclay
username@saclay:~$ iotlab-experiment wait

    Make a note of the displayed experiment ID, then get the allocated node IDs once the experiment is running by using the commands below to retrieve additional information about the experiment:

    username@saclay:~$ iotlab-experiment get -i <experiment_ID> -s
username@saclay:~$ iotlab-experiment get -i <experiment_ID> -r

  3. The first node (a8-1 in our example) will act as a border router using the gnrc_border_router code. To set up its firmware, follow the instructions below:

    • Clone the RIOT OS repository from GitHub:

       username@saclay:~$ git clone https://github.com/RIOT-OS/RIOT.git

    • Build the gnrc_border_router firmware with the appropriate baud rate for A8-M3 nodes, which is 500,000:

       username@saclay:~$ source /opt/riot.source
 username@saclay:~$ cd RIOT
 username@saclay:~/RIOT/$ make ETHOS_BAUDRATE=500000 BOARD=iotlab-a8-m3 clean all -C examples/gnrc_border_router

    • Copy and flash the compiled firmware to the first experiment node by running the following commands:

       username@saclay:~/RIOT/$ scp examples/gnrc_border_router/bin/iotlab-a8-m3/gnrc_border_router.elf root@node-a8-1:
 username@saclay:~/RIOT/$ ssh root@node-a8-1
 root@node-a8-1:~# flash_a8_m3 gnrc_border_router.elf

  4. Configure the network settings of the border router, as follows:

    • Use the first node to compile the tool named uhcpd (Micro Host Configuration Protocol):

       root@node-a8-1:~# cd ~/A8/riot/RIOT/dist/tools/uhcpd
 root@node-a8-1:~/A8/riot/RIOT/dist/tools/uhcpd# make clean all

    • Also compile the tool named ethos (Ethernet Over Serial) and configure the public IPv6 network of the node:

       root@node-a8-1:~/A8/riot/RIOT/dist/tools/uhcpd# cd ../ethos
 root@node-a8-1:~/A8/riot/RIOT/dist/tools/ethos# make clean all
 root@node-a8-1:~/A8/riot/RIOT/dist/tools/ethos# ./start_network.sh /dev/ttyA8_M3 tap0 2001:660:3207:401::/64 500000

      Output similar to that shown below will be displayed.

       net.ipv6.conf.tap0.forwarding = 1
 net.ipv6.conf.tap0.accept_ra = 0
 ----> ethos: sending hello.
 ----> ethos: activating serial pass through.
 ----> ethos: hello reply received

  5. In another terminal, connect to the second node (a8-2 in our example) to configure and start the MQTT broker:

    • Connect to the Saclay SSH frontend, then to second node:

       your_computer:~$ ssh <username>@saclay.iot-lab.info
 username@saclay:~$ ssh root@node-a8-2

    • Edit the configuration file config.conf (e.g., by using the vim editor) to add the following content:

       # Enable debugging output
 trace_output protocol

 # Listen for MQTT-SN traffic on UDP port 1885
 listener 1885 INADDR_ANY mqtts
 ipv6 true

 # Listen to MQTT connections on TCP port 1886
 listener 1886 INADDR_ANY
 ipv6 true

      This configuration will make the MQTT broker reachable from any node behind the border router using MQTT-SN on port 1885, and from the SSH frontend using MQTT on port 1886.

    • Get the global IPv6 address of this node, as it will be needed later to connect to it at step 6:

       root@node-a8-2:~# ip -6 -o addr show eth0
 2: eth0    inet6 2001:660:3207:400::66/64 scope global        valid_lft forever preferred_lft forever
 2: eth0    inet6 fe80::fadc:7aff:fe01:98fc/64 scope link      valid_lft forever preferred_lft forever

    • Start the MQTT broker on the second node:

       root@node-a8-2:~# broker_mqtts config.conf

      The output will be similar to that shown below.

       20170715 001526.077 CWNAN9999I Really Small Message Broker
 20170715 001526.084 CWNAN9998I Part of Project Mosquitto in Eclipse
 (http://projects.eclipse.org/projects/technology.mosquitto)
 20170715 001526.088 CWNAN0049I Configuration file name is config.conf
 20170715 001526.099 CWNAN0053I Version 1.3.0.2, Jul 11 2017 14:55:20
 20170715 001526.102 CWNAN0054I Features included: bridge MQTTS
 20170715 001526.104 CWNAN9993I Authors: Ian Craggs (icraggs@uk.ibm.com), Nicholas O'Leary
 20170715 001526.111 CWNAN0300I MQTT-S protocol starting, listening on port 1885
 20170715 001526.115 CWNAN0014I MQTT protocol starting, listening on port 1886

  6. Open a third terminal to prepare the third node (a8-3 in our example) as an MQTT-SN client:

    • Log in to the Saclay SSH frontend, build and flash the RIOT MQTT-SN firmware:

       your_computer$ ssh <username>@saclay.iot-lab.info
 username@saclay:~$ source /opt/riot.source
 username@saclay:~$ cd RIOT
 username@saclay:~/RIOT$ make BOARD=iotlab-a8-m3 -C examples/emcute_mqttsn
 username@saclay:~/RIOT/$ scp examples/emcute_mqttsn/bin/iotlab-a8-m3/emcute_mqttsn.elf root@node-a8-3:
 username@saclay:~/RIOT/$ ssh root@node-a8-3
 root@node-a8-3:~# flash_a8_m3 emcute_mqttsn.elf

    • Use the program miniterm.py to access the shell interface of the third node, then type "help":

       root@node-a8-3:~# miniterm.py /dev/ttyA8_M3 500000 -e
 --- Miniterm on /dev/ttyA8_M3  500000,8,N,1 ---
 --- Quit: Ctrl+] | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
 help

      The following command menu will be displayed:

       Description
 ---------------------------------------
 con                  connect to MQTT broker
 discon               disconnect from the current broker
 pub                  publish something
 sub                  subscribe topic
 unsub                unsubscribe from topic
 will                 register a last will
 reboot               Reboot the node
 ps                   Prints information about running threads
 ping6                Ping via ICMPv6
 random_init          initializes the PRNG
 random_get           returns 32 bit of pseudo randomness
 ifconfig             Configure network interfaces
 ncache               manage neighbor cache by hand
 routers              IPv6 default router list

    • Use the con command to connect to the MQTT broker by specifying its global IPv6 address retrieved at step 5, then subscribe to the test/riot topic using the command sub:

       > con 2001:660:3207:400::66 1885
 > sub test/riot

  7. Use a fourth terminal to test the publish/subscribe mechanism between the MQTT broker and client nodes:

    • Connect to the Saclay SSH frontend and use the preinstalled mosquitto_pub command to publish the message "iotrain-lab" to the MQTT broker by using its global IPv6 address determined at step 5 and the topic name test/riot:

       your_computer$ ssh <username>@saclay.iot-lab.info
 username@saclay:~$ mosquitto_pub -h 2001:660:3207:400::66 -p 1886 -t test/riot -m iotrain-lab

    • In the third terminal (used at step 6), the MQTT-SN client that already subscribed to the topic test/riot should produce the following output:

       ### got publication for topic 'test/riot' [1] ###
 iotrain-lab

    • Next you can try using the mosquitto_sub command on the SSH frontend (fourth terminal) to subscribe, and the pub command on the MQTT-SN client (third terminal) to exchange messages in the opposite direction.

Note

We noticed that the miniterm.py program used at step 6 is unstable occasionally, and may quit unexpectedly; please repeat the procedure if this happens. This issue seems to be related to the software tools provided by FIT/IoT-Lab, and we hope that it will be fixed soon.