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CoAP Protocol

  • Classification: Fundamental Training > Protocols
  • Nodes: M3 x 2
  • Difficulty: High

Overview

CoAP (Constrained Application Protocol) is a specialized web transfer protocol used with constrained nodes and networks in the Internet of Things. The protocol is designed for machine-to-machine (M2M) applications, such as smart energy and building automation.

In this exercise you will learn about the basics of CoAP using RIOT OS and leveraging the gnrc_border_router and microcoap_server examples provided in the RIOT OS repository on GitHub.

Tutorial

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

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

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

    username@grenoble:~$ iotlab-auth -u <username>
username@grenoble:~$ iotlab-experiment submit -n riot_coap -d 60 -l 2,archi=m3:at86rf231+site=grenoble
username@grenoble:~$ 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@grenoble:~$ iotlab-experiment get -i <experiment_ID> -s
username@grenoble:~$ iotlab-experiment get -i <experiment_ID> -r

  3. The first node (m3-1 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@grenoble:~$ git clone https://github.com/RIOT-OS/RIOT.git

    • Build the gnrc_border_router firmware with the appropriate baud rate for M3 nodes, which is 500,000; to minimize radio interference with other experiments, you can use a different 802.15.4 channel than the default value 26 by adding the DEFAULT_CHANNEL option to the make command below:

       username@grenoble:~$ source /opt/riot.source
 username@grenoble:~$ cd RIOT
 username@grenoble:~/RIOT/$ make ETHOS_BAUDRATE=500000 DEFAULT_CHANNEL=20 BOARD=iotlab-m3 -C examples/gnrc_border_router clean all

    • Flash the compiled firmware to the first experiment node by running the following command:

       username@grenoble:~/RIOT/$ iotlab-node --update examples/gnrc_border_router/bin/iotlab-m3/gnrc_border_router.elf -l grenoble,m3,1

  4. Configure the network settings of the border router and propagate an IPv6 prefix by using the command ethos_uhcpd.py:

    username@grenoble:~$ sudo ethos_uhcpd.py m3-1 tap0 2001:660:5307:3100::1/64

    If the command above fails, check whether the tap0 network interface is not already in use, as you may need to choose another one. If you see the error "overlaps with routes", another experiment is using the same IPv6 prefix (e.g., 2001:660:5307:3100::1/64), so you need to change it (more information about the IPv6 support in FIT/IoT-LAB is available here). To view the currently used IPv6 prefixes, run the command ip -6 route on the SSH frontend; the output will look similar to that shown below.

    2001:660:5307:30fff::/64 dev eth0  proto kernel  metric 256  mtu 1500 advmss 1440 hoplimit 4294967295
2001:660:5307:3100::/64 dev tun0  proto kernel  metric 256  mtu 1500 advmss 1440 hoplimit 4294967295
fe80::/64 dev eth1  proto kernel  metric 256  mtu 1500 advmss 1440 hoplimit 4294967295
fe80::/64 dev eth0  proto kernel  metric 256  mtu 1500 advmss 1440 hoplimit 4294967295
fe80::/64 dev tun0  proto kernel  metric 256  mtu 1500 advmss 1440 hoplimit 4294967295
default via 2001:660:5307:30ff:ff:: dev eth0  metric 1  mtu 1500 advmss 1440 hoplimit 4294967295

    When the border router network is correctly configured, the ethos_uhcpd.py command output should be as shown below:

    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 again to the Grenoble SSH frontend and set up the other experiment node (m3-2 in our example) using the RIOT microcoap_server code:

    • Compile the firmware (if you changed the default channel, make sure to use the same setting for the make command below):

       your_computer:~$ ssh <username>@grenoble.iot-lab.info
 username@grenoble:~$ source /opt/riot.source
 username@grenoble:~$ cd RIOT
 username@grenoble:~/RIOT/$ make DEFAULT_CHANNEL=<channel> BOARD=iotlab-m3 -C examples/microcoap_server clean all``

    • Flash the compiled firmware to the second experiment node by running the following command:

       username@grenoble:~/RIOT/$ iotlab-node --update examples/microcoap_server/bin/iotlab-m3/microcoap_server.elf -l grenoble,m3,2

  6. Use the shell interface of the border router to find out the IPv6 address of the node running the CoAP server. For this purpose, type "Enter" in the terminal of where you ran the ethos_uhcpd.py script to access the RIOT shell, then type the command nib neigh:

    > help
help
Command              Description
---------------------------------------
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
nib                  Configure neighbor information base
ifconfig             Configure network interfaces
fibroute             Manipulate the FIB (info: 'fibroute [add|del]')
6ctx                 6LoWPAN context configuration tool

> nib neigh
nib neigh
[...]
2001:660:3207:4c1:1711:6b10:65fd:bd36 dev #6 lladdr 15:11:6b:10:65:fd:bd:36  STALE REGISTERED

  7. In a new terminal log in to the Grenoble SSH frontend, and use the coap command to query the CoAP server and confirm that it is operating correctly. By default, the CoAP server of RIOT exposes only the board type to a CoAP GET request on /riot/board. To get this information run the following command (make sure to use the CoAP server address identified at step 6 above):

    username@grenoble:~$ coap get coap://[2001:660:3207:4c1:1711:6b10:65fd:bd36]/riot/board
(2.05)	iotlab-m3