Telemetry Data on Google Cloud using Pub/Sub, IoT Core and DTN

This project has been developed by Dr Lara Suzuki 👩‍💻 and supervised by Vint Cerf 🧑‍💻, both at Google Inc.

In this tutorial we will demonstrate how to connect a Raspberry Pi and Sensor Hat onto Google Cloud using cloud Pub/Sub on host 1 and serving the messages over DTN to host 2. This tutorial follows the Running DTN on Google Cloud using a Two-Node Ring tutorial and uses the configurations of host 1 and host 2 as described in the rc files of that repo.

Setting up Raspbberry Pi and the Sense Hat

In this tutorial we use Raspberry Pi 4 model B (2018) and Sense Hat Version 1.0.

The first step is to be sure your Pi can connect to the Internet. You can either plug in an ethernet cable, or if you’re using WiFi, scan for networks your Pi can see. Plug your Pi in a monitor, and when it starts, at the top right corner you can find the wifi logo. Select the network you want to connect to. Once that is connected open your browser to check whether you can access the Internet.

Library dependency setup

The first thing to do is to make sure that the places where Raspberry Pi will be getting its libraries from is current. For this, on your Pi’s terminal, run the following command:

$ sudo apt-get update

The next step is to securely connect to Google Cloud IoT Core. For this we will use JWT to handle authentication (library pyjwt). The meta-model for communication used on the Google Cloud Pub/Sub is based on publish/subscribe messaging technology provided by the MQTT (MQ Telemetry Transport) protocol (library paho-mqtt). MQTT is a topic-based publish/subscribe communications protocol that is designed to be open, simple, lightweight, easy-to-implement, and efficient in terms of processor, memory, and network resources.

On your Pi’s terminal run the following commands

$ sudo apt-get install build-essential
$ sudo apt-get install libssl-dev
$ sudo apt-get install python-dev
$ sudo apt-get install libffi-dev
$ sudo pip install paho-mqtt

For encryption, run the install the pyjwt library and its dependency, the cryptography library .

$ sudo pip install pyjwt
$ sudo pip install cryptography

For telemetry data we are using Sense Hat. Sense Hat is composed by telemetry sensors such as temperature, accelerometer, humidity and pressure. To install the library for Sense Hat, run the command:

$ sudo apt get install sense-hat

SSL Certificate — RSA with X509 wrapper

In order to authenticate in Google Cloud IoT Core, we need a SSL certificate. We will create an RSA with X509 wrapper. For this, execute the following command on your Pi’s terminal:

$ openssl req -x509 -newkey rsa:2048 -keyout sensing_private.pem -nodes -out demo.pub -subj “/CN=unused”

Setting up Google Cloud Platform

The First step is to enable Cloud IoT on Google Cloud. If you followed the instructions of tutorial DTN 101 — Running the Interplanetary Internet on Google Cloud, you will already have Cloud IoT enabled. If not, once you open Google Cloud Console, at the search bar type IoT Core. Once a the IoT page is loaded, click Enable so that the appropriate permissions are granted.

Setting up your Pi on Google Cloud IoT Core and Pub/Sub

Once IoT Core is enabled, at the top left corner, click on the hamburger icon, scrow down until you find IoT Core. A page of Registries will open. The following steps demonstrates how to create a Registry for your Raspberry Pi on Google IoT Core.

1. Click on Create Registry
2. Give an id for your registry. In our case we called it terrestrial-station
3. Select the region closest to you
4. Under Cloud Pub/Sub topics, in the dropdown menu, select Create a Topic
5. In the pop-up window type a name for your topic. In our case we gave the topic name sensing
6. Back in the dropdown menu, select the topic you have just created
7. Hit Create

Back in the registry window you will see that your registry, terrestrial-station has been created. To register your Raspberry Pi on the registry, follow the steps below:

1. Click on the terrestrial-station registry
2. Under IoT Core click Devices
3. At the top of the page, click Create a Device
4. Give an id to your device. In our case we named it as sensing-hat
5. Click on the link Communication, Cloud Logging, Authentication
6. Under Authentication, select Public Key Format RS256_X509
7. To confirm that your Pi is okay to send messages to Google IoT Core, in the Public Key Value text box, paste the value of your Pi's public key

To copy the content of your Pi’s public key, on the Pi’s terminal run:

$ cat demo.pub

Copy everything, including the tages, between

-----BEGIN PUBLIC KEY-----
-----END PUBLIC KEY-----

and paste it in the Public Key Value textbox.

Finally, the last security configuration is to obtail the Google roots.pem file so your device knows it’s communicating with Google Cloud IoT Core. On the Pi run

$ wget https://pki.google.com/roots.pem

Create a Subscription to listen to the Pub/Sub Topic

On the Google Cloud Console, type Pub/Sub on the search bar, or pick up from the hamburger menu on the top left side of the window. Follow the steps below to create a subscription to listen to the topic sensing:

1. Click Create Subscription
2. Give an id to your subscription. In our case we named it listener
3. On the dropdown menu select the topic you created (in our case: sensing)
4. Click Create

Now you have all the pieces needed to send telemetry data from your Pi to Google Cloud IoT Core!

Send telemetry data from Raspberry Pi to Google Cloud

The code on this repository named sense.py is based on the implementation of GabeWeiss.

In the code, edit the following fields:

ssl_private_key_filepath = '/home/pi/sensing_private.pem'
ssl_algorithm = 'RS256'
root_cert_filepath = '/home/pi/roots.pem'
project_id = 'dtn-host-iot-297209'
gcp_location = 'us-central1'
registry_id = 'terrestrial-station'
device_id = 'sensing-hat'

Once you have configured the above parameters in the file sense.py, on your Raspberry Pi run the command:

$ python3 sense.py

Send telemetry data to from host 1 to host 2 via DTN

Log into the VM host 1. In the VM go to the base directory of ION and create a folder named dtn

$ mkdir dtn

CD into dtn directory, and clone the file named iot.py. In this file configure the following parameters:

subscription_path = subscriber.subscription_path(
  'ID_OF_YOUR_GOOGLE_CLOUD_PROJECT', 'ID_OF_YOUR_SUBSCRIPTION')

And add host 2 as the receiver of the telemetry data:

os.system(f'echo "{value}" | bpsource ipn:2.1')

On the terminal of host 1 and host 2, start ion:

$ ionstart -I hostX.rc #where X is the number of the host

On the terminal of host 2, start bpsink

$ bpsink ipn:2.1 &

On the terminal of host 1, start iot.py

$ python3 iot.py

On the terminal of host 1 you should see the print out of the telemetry data received as below:

On the terminal of host 2 you should see the payloads delivered. Please note that messages beyond 80 characters are not shown on bpsink: