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FIWARE IoT Agents License: MIT Support badge UltraLight 2.0
Documentation

This tutorial uses introduces the use of the MQTT protocol across IoT devices connecting to FIWARE. The UltraLight 2.0 IoT Agent created in the previous tutorial is reconfigured to communicate with a set of dummy IoT devices using MQTT via a Mosquitto message broker

The tutorial uses cUrl commands throughout, but is also available as Postman documentation

Run in Postman Open in Gitpod

  • このチュートリアルは日本語でもご覧いただけます。

Contents

Details

What is MQTT?

"With the technology at our disposal, the possibilities are unbounded. All we need to do is make sure we keep talking."

— Stephen Hawking

"MQTT is a publish-subscribe-based messaging protocol used in the internet of Things. It works on top of the TCP/IP protocol, and is designed for connections with remote locations where a "small code footprint" is required or the network bandwidth is limited. The goal is to provide a protocol, which is bandwidth-efficient and uses little battery power."1

The previous tutorial used HTTP as its transport mechanism between the devices and the IoT Agent. HTTP uses a request/response paradigm where each device connects directly to the IoT Agent. MQTT is different in that publish-subscribe is event-driven and pushes messages to clients. It requires an additional central communication point (known as the MQTT broker) which it is in charge of dispatching all messages between the senders and the rightful receivers. Each client that publishes a message to the broker, includes a topic into the message. The topic is the routing information for the broker. Each client that wants to receive messages subscribes to a certain topic and the broker delivers all messages with the matching topic to the client. Therefore the clients don’t have to know each other, they only communicate over the topic. This architecture enables highly scalable solutions without dependencies between the data producers and the data consumers.

A summary of the differences between the two transport protocols can be seen below:

HTTP Transport MQTT Transport
IoT Agent communicates with IoT devices directly IoT Agent communicates with IoT devices indirectly via an MQTT Broker
Request-Response Paradigm Publish-Subscribe Paradigm
IoT Devices must always be ready to receive communication IoT Devices choose when to receive communication
Higher Power Requirement Low Power Requirement

The UltraLight 2.0 IoT Agent will only send or interpret messages using the UltraLight 2.0 syntax, however it can be used to send and receive messages over multiple transport mechanisms. Therefore we are able to use the same FIWARE generic enabler to connect to a wider range of IoT devices.

Mosquitto MQTT Broker

Mosquitto is a readily available, open source MQTT broker which will be used during this tutorial. It is available licensed under EPL/EDL. More information can be found at https://mosquitto.org/

Device Monitor

For the purpose of this tutorial, a series of dummy IoT devices have been created, which will be attached to the context broker. Details of the architecture and protocol used can be found in the IoT Sensors tutorial The state of each device can be seen on the UltraLight device monitor web page found at: http://localhost:3000/device/monitor

FIWARE Monitor

Architecture

This application builds on the components created in previous tutorials. It will make use of two FIWARE components - the Orion Context Broker and the IoT Agent for UltraLight 2.0. Usage of the Orion Context Broker is sufficient for an application to qualify as “Powered by FIWARE”. Both the Orion Context Broker and the IoT Agent rely on open source MongoDB technology to keep persistence of the information they hold. We will also be using the dummy IoT devices created in the previous tutorial Additionally we will add an instance of the Mosquitto MQTT broker which is open source and available under the EPL/EDL.

Therefore the overall architecture will consist of the following elements:

  • The FIWARE Orion Context Broker which will receive requests using NGSI-v2
  • The FIWARE IoT Agent for UltraLight 2.0 which will:
    • receive southbound requests using NGSI-v2 and convert them to UltraLight 2.0 MQTT topics for the MQTT Broker
    • listen to the MQTT Broker on registered topics to send measurements northbound
  • The Mosquitto MQTT Broker which acts as a central communication point, passing MQTT topics between the IoT Agent and IoT devices as necessary.
  • The underlying MongoDB database :
    • Used by the Orion Context Broker to hold context data information such as data entities, subscriptions and registrations
    • Used by the IoT Agent to hold device information such as device URLs and Keys
  • A webserver acting as set of dummy IoT devices using the UltraLight 2.0 protocol running over MQTT.
  • The Context Provider NGSI proxy is not used in this tutorial. It does the following:
    • receive requests using NGSI-v2
    • makes requests to publicly available data sources using their own APIs in a proprietary format
    • returns context data back to the Orion Context Broker in NGSI-v2 format.
  • The Stock Management Frontend is not used in this tutorial will it does the following:
    • Display store information
    • Show which products can be bought at each store
    • Allow users to "buy" products and reduce the stock count.

Since all interactions between the elements are initiated by HTTP or MQTT requests over TCP, the entities can be containerized and run from exposed ports.

The necessary configuration information for wiring up the Mosquitto MQTT Broker, the IoT devices and the IoT Agent can be seen in the services section of the associated docker-compose.yml file:

Mosquitto Configuration

mosquitto:
    image: eclipse-mosquitto
    hostname: mosquitto
    container_name: mosquitto
    networks:
        - default
    expose:
        - "1883"
        - "9001"
    ports:
        - "1883:1883"
        - "9001:9001"
    volumes:
        - ./mosquitto/mosquitto.conf:/mosquitto/config/mosquitto.conf

The mosquitto container is listening on two ports:

  • Port 1883 is exposed so we can post MQTT topics
  • Port 9001 is the standard port for HTTP/Websocket communications

The attached volume is a configuration file used to increase the debug level of the MQTT Message Broker.

Dummy IoT Devices Configuration

tutorial:
    image: fiware/tutorials.context-provider
    hostname: iot-sensors
    container_name: fiware-tutorial
    networks:
        - default
    expose:
        - "3000"
        - "3001"
    ports:
        - "3000:3000"
        - "3001:3001"
    environment:
        - "DEBUG=tutorial:*"
        - "WEB_APP_PORT=3000"
        - "DUMMY_DEVICES_PORT=3001"
        - "DUMMY_DEVICES_API_KEY=4jggokgpepnvsb2uv4s40d59ov"
        - "DUMMY_DEVICES_TRANSPORT=MQTT"

The tutorial container is listening on two ports:

  • Port 3000 is exposed so we can see the web page displaying the Dummy IoT devices.
  • Port 3001 is exposed purely for tutorial access - so that cUrl or Postman can make UltraLight commands without being part of the same network.

The tutorial container is driven by environment variables as shown:

Key Value Description
DEBUG tutorial:* Debug flag used for logging
WEB_APP_PORT 3000 Port used by web-app which displays the dummy device data
DUMMY_DEVICES_PORT 3001 Port used by the dummy IoT devices to receive commands
DUMMY_DEVICES_API_KEY 4jggokgpepnvsb2uv4s40d59ov Random security key used for UltraLight interactions - used to ensure the integrity of interactions between the devices and the IoT Agent
DUMMY_DEVICES_TRANSPORT MQTT The transport protocol used by the dummy IoT devices

The other tutorial container configuration values described in the YAML file are not used in this tutorial.

IoT Agent for UltraLight 2.0 Configuration

The IoT Agent for UltraLight 2.0 can be instantiated within a Docker container. An official Docker image is available from Docker Hub tagged fiware/iotagent-ul. The necessary configuration can be seen below:

iot-agent:
    image: fiware/iotagent-ul:latest
    hostname: iot-agent
    container_name: fiware-iot-agent
    depends_on:
        - mongo-db
    networks:
        - default
    expose:
        - "4041"
    ports:
        - "4041:4041"
    environment:
        - IOTA_CB_HOST=orion
        - IOTA_CB_PORT=1026
        - IOTA_NORTH_PORT=4041
        - IOTA_REGISTRY_TYPE=mongodb
        - IOTA_LOG_LEVEL=DEBUG
        - IOTA_TIMESTAMP=true
        - IOTA_CB_NGSI_VERSION=v2
        - IOTA_AUTOCAST=true
        - IOTA_MONGO_HOST=mongo-db
        - IOTA_MONGO_PORT=27017
        - IOTA_MONGO_DB=iotagentul
        - IOTA_PROVIDER_URL=http://iot-agent:4041
        - IOTA_MQTT_HOST=mosquitto
        - IOTA_MQTT_PORT=1883

The iot-agent container relies on the presence of the Orion Context Broker and uses a MongoDB database to hold device information such as device URLs and Keys. The container is listening on a single port:

  • Port 4041 is exposed purely for tutorial access - so that cUrl or Postman can make provisioning commands without being part of the same network.

The iot-agent container is driven by environment variables as shown:

Key Value Description
IOTA_CB_HOST orion Hostname of the context broker to update context
IOTA_CB_PORT 1026 Port that context broker listens on to update context
IOTA_NORTH_PORT 4041 Port used for Configuring the IoT Agent and receiving context updates from the context broker
IOTA_REGISTRY_TYPE mongodb Whether to hold IoT device info in memory or in a database
IOTA_LOG_LEVEL DEBUG The log level of the IoT Agent
IOTA_TIMESTAMP true Whether to supply timestamp information with each measurement received from attached devices
IOTA_CB_NGSI_VERSION v2 Whether to supply use NGSI v2 when sending updates for active attributes
IOTA_AUTOCAST true Ensure Ultralight number values are read as numbers not strings
IOTA_MONGO_HOST context-db The hostname of mongoDB - used for holding device information
IOTA_MONGO_PORT 27017 The port mongoDB is listening on
IOTA_MONGO_DB iotagentul The name of the database used in mongoDB
IOTA_PROVIDER_URL http://iot-agent:4041 URL passed to the Context Broker when commands are registered, used as a forwarding URL location when the Context Broker issues a command to a device
IOTA_MQTT_HOST mosquitto The hostname of the MQTT Broker
IOTA_MQTT_PORT 1883 The port the MQTT Broker is listening on to receive topics

As you can see, use of the MQTT transport is driven by only two environment variables IOTA_MQTT_HOST and IOTA_MQTT_PORT

Prerequisites

Docker and Docker Compose

To keep things simple all components will be run using Docker. Docker is a container technology which allows to different components isolated into their respective environments.

  • To install Docker on Windows follow the instructions here
  • To install Docker on Mac follow the instructions here
  • To install Docker on Linux follow the instructions here

Docker Compose is a tool for defining and running multi-container Docker applications. A YAML file is used configure the required services for the application. This means all container services can be brought up in a single command. Docker Compose is installed by default as part of Docker for Windows and Docker for Mac, however Linux users will need to follow the instructions found here

You can check your current Docker and Docker Compose versions using the following commands:

docker-compose -v
docker version

Please ensure that you are using Docker version 20.10 or higher and Docker Compose 1.29 or higher and upgrade if necessary.

Cygwin for Windows

We will start up our services using a simple Bash script. Windows users should download cygwin to provide a command-line functionality similar to a Linux distribution on Windows.

Start Up

Before you start you should ensure that you have obtained or built the necessary Docker images locally. Please clone the repository and create the necessary images by running the commands as shown:

git clone https://github.com/FIWARE/tutorials.IoT-over-MQTT.git
cd tutorials.IoT-over-MQTT
git checkout NGSI-v2

./services create

Thereafter, all services can be initialized from the command-line by running the services Bash script provided within the repository:

./services start

ℹ️ Note: If you want to clean up and start over again you can do so with the following command:

./services stop

Provisioning an IoT Agent (UltraLight over MQTT)

To follow the tutorial correctly please ensure you have the device monitor page available in your browser and click on the page to enable audio before you enter any cUrl commands. The device monitor displays the current state of an array of dummy devices using Ultralight 2.0 syntax

Device Monitor

The device monitor can be found at: http://localhost:3000/device/monitor

Checking Mosquitto Health

We will start by mimicking the roles of both the IoT Agent and a dummy IoT device and send and receive some messages using MQTT. This section of the tutorial requires several open terminals.

Start an MQTT Subscriber (:one:st Terminal)

Eventually once we have wired by the system correctly, IoT Agent will subscribe to all relevant events to listen for northbound traffic in the form of sensor measurements. It therefore will need to make a subscription across all topics. Similarly an actuator must subscribe to a single topic to receive events which effect itself when commands are sent southbound. To check that the lines of communication are open, we can subscribe to a given topic, and see that we are able to receive something when a message is published.

Open a new terminal, and create a new running mqtt-subscriber Docker container as follows:

docker run -it --rm --name mqtt-subscriber \
  --network fiware_default efrecon/mqtt-client sub -h mosquitto -t "/#"

The terminal will then be ready to receive events

Start an MQTT Publisher (:two:nd Terminal)

A sensor sending northbound measurements will publish to those measurements to the MQTT Broker to be passed on to any subscriber than wants them. The sensor will not need to make a connection to the subscriber directly.

Open a new terminal, and run a mqtt-publisher Docker container to send a message as follows:

docker run -it --rm --name mqtt-publisher \
  --network fiware_default efrecon/mqtt-client pub -h mosquitto -m "HELLO WORLD" -t "/test"

1️⃣st terminal - Result:

If the MQTT Broker is functioning correctly, the message should be received in the other terminal

HELLO WORLD

Stop an MQTT Subscriber (:two:nd Terminal)

To terminate the MQTT subscriber, run the following Docker command:

docker stop mqtt-subscriber

Show Mosquitto Log

To show that the communication occurred via the MQTT Broker, we can inspect the log of the mosquitto Docker container as shown:

docker logs --tail 10 mosquitto

Result:

1529661883: New client connected from 172.18.0.5 as mqttjs_8761e518 (c1, k0).
1529662472: New connection from 172.18.0.7 on port 1883.
1529662472: New client connected from 172.18.0.7 as mosqpub|1-5637527c63c1 (c1, k60).
1529662472: Client mosqpub|1-5637527c63c1 disconnected.
1529662614: New connection from 172.18.0.7 on port 1883.
1529662614: New client connected from 172.18.0.7 as mosqsub|1-64b27d675f58 (c1, k60).
1529662623: New connection from 172.18.0.8 on port 1883.
1529662623: New client connected from 172.18.0.8 as mosqpub|1-ef03e74b0270 (c1, k60).
1529662623: Client mosqpub|1-ef03e74b0270 disconnected.
1529667841: Socket error on client mosqsub|1-64b27d675f58, disconnecting.

Checking the IoT Agent Service Health

You can check if the IoT Agent is running by making an HTTP request to the exposed port:

1️⃣ Request:

curl -X GET \
  'http://localhost:4041/iot/about'

The response will look similar to the following:

{
    "libVersion": "2.6.0-next",
    "port": "4041",
    "baseRoot": "/",
    "version": "1.6.0-next"
}

What if I get a Failed to connect to localhost port 4041: Connection refused Response?

If you get a Connection refused response, the IoT Agent cannot be found where expected for this tutorial - you will need to substitute the URL and port in each cUrl command with the corrected IP address. All the cUrl commands tutorial assume that the IoT Agent is available on localhost:4041.

Try the following remedies:

  • To check that the docker containers are running try the following:
docker ps

You should see four containers running. If the IoT Agent is not running, you can restart the containers as necessary. This command will also display open port information.

  • If you have installed docker-machine and Virtual Box, the context broker, IoT Agent and Dummy Device docker containers may be running from another IP address - you will need to retrieve the virtual host IP as shown:
curl -X GET \
 'http://$(docker-machine ip default):4041/version'

Alternatively run all your curl commands from within the container network:

docker run --network fiware_default --rm appropriate/curl -s \
 -X GET 'http://iot-agent:4041/iot/about'

Connecting IoT Devices

The IoT Agent acts as a middleware between the IoT devices and the context broker. It therefore needs to be able to create context data entities with unique IDs. Once a service has been provisioned and an unknown device makes a measurement the IoT Agent add this to the context using the supplied <device-id> (unless the device is recognized and can be mapped to a known ID.

There is no guarantee that every supplied IoT device <device-id> will always be unique, therefore all provisioning requests to the IoT Agent require two mandatory headers:

  • fiware-service header is defined so that entities for a given service can be held in a separate mongoDB database.
  • fiware-servicepath can be used to differentiate between arrays of devices.

For example within a smart city application you would expect different fiware-service headers for different departments (e.g. parks, transport, refuse collection etc.) and each fiware-servicepath would refer to specific park and so on. This would mean that data and devices for each service can be identified and separated as needed, but the data would not be siloed - for example data from a Smart Bin within a park can be combined with the GPS Unit of a refuse truck to alter the route of the truck in an efficient manner.

The Smart Bin and GPS Unit are likely to come from different manufacturers and it cannot be guaranteed that there is no overlap within <device-id>s used. The use of the fiware-service and fiware-servicepath headers can ensure that this is always the case, and allows the context broker to identify the original source of the context data.

Provisioning a Service Group for MQTT

Invoking group provision is always the first step in connecting devices. For MQTT communication, provisioning supplies the authentication key so the IoT Agent will know which topic it must subscribe to.

It is possible to set up default commands and attributes for all devices as well, but this is not done within this tutorial as we will be provisioning each device separately.

This example provisions an anonymous group of devices. It tells the IoT Agent that a series of devices will be communicating by sending device measures over the /ul/4jggokgpepnvsb2uv4s40d59ov topic

Note Measures and commands are sent over different MQTT topics:

  • Measures are sent on the /<protocol>/<api-key>/<device-id>/attrs topic
  • Commands are sent on the /<api-key>/<device-id>/cmd topic

The reasoning behind this is that when sending measures northbound from device to IoT Agent, it is necessary to explicitly identify which IoT Agent is needed to parse the data. This is done by prefixing the relevant MQTT topic with a protocol, otherwise there is no way to define which agent is processing the measure. This mechanism allows smart systems to connect different devices to different IoT Agents according to need.

For southbound commands, this distinction is unnecessary since the correct IoT Agent has already registered itself for the command during the device provisioning step and the device will always receive commands in an appropriate format.

The resource attribute is left blank since HTTP communication is not being used. The URL location of cbroker is an optional attribute - if it is not provided, the IoT Agent uses the default context broker URL as defined in the configuration file, however it has been added here for completeness.

2️⃣ Request:

curl -iX POST \
  'http://localhost:4041/iot/services' \
  -H 'Content-Type: application/json' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /' \
  -d '{
 "services": [
   {
     "apikey":      "4jggokgpepnvsb2uv4s40d59ov",
     "cbroker":     "http://orion:1026",
     "entity_type": "Thing",
     "resource":    ""
   }
 ]
}'

Provisioning a Sensor

It is common good practice to use URNs following the NGSI-LD specification when creating entities. Furthermore it is easier to understand meaningful names when defining data attributes. These mappings can be defined by provisioning a device individually.

Three types of measurement attributes can be provisioned:

  • attributes are active readings from the device
  • lazy attributes are only sent on request - The IoT Agent will inform the device to return the measurement
  • static_attributes are as the name suggests static data about the device (such as relationships) passed on to the context broker.

Note: in the case where individual ids are not required, or aggregated data is sufficient the attributes can be defined within the provisioning service rather than individually.

3️⃣ Request:

curl -iX POST \
  'http://localhost:4041/iot/devices' \
  -H 'Content-Type: application/json' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /' \
  -d '{
 "devices": [
   {
     "device_id":   "motion001",
     "entity_name": "urn:ngsi-ld:Motion:001",
     "entity_type": "Motion",
     "protocol":    "PDI-IoTA-UltraLight",
     "transport":   "MQTT",
     "timezone":    "Europe/Berlin",
     "attributes": [
       { "object_id": "c", "name": "count", "type": "Integer" }
     ],
     "static_attributes": [
       { "name":"refStore", "type": "Relationship", "value": "urn:ngsi-ld:Store:001"}
     ]
   }
 ]
}
'

In the request we are associating the device motion001 with the URN urn:ngsi-ld:Motion:001 and mapping the device reading c with the context attribute count (which is defined as an Integer) A refStore is defined as a static_attribute, placing the device within Store urn:ngsi-ld:Store:001.

The addition of the transport=MQTT attribute in the body of the request is sufficient to tell the IoT Agent that it should subscribe to the /<api-key>/<device-id> topic to receive measurements.

You can simulate a dummy IoT device measurement coming from the Motion Sensor device motion001, by posting an MQTT message to the following topic

4️⃣ MQTT Request:

docker run -it --rm --name mqtt-publisher --network \
  fiware_default efrecon/mqtt-client pub -h mosquitto -m "c|1" \
  -t "/ul/4jggokgpepnvsb2uv4s40d59ov/motion001/attrs"
  • The value of the -m parameter defines the message. This is in UltraLight syntax.
  • The value of the -t parameter defines the topic.

The topic must be in the following form:

/<protocol>/<api-key>/<device-id>/attrs

Note In the previous tutorial, when testing HTTP connectivity between the Motion Sensor and an IoT Agent, a similar dummy HTTP request was sent to update the count value. This time the IoT Agent is configured to listen to MQTT topics, and we need to post a dummy message to an MQTT topic.

When using the MQTT transport protocol, the IoT Agent is subscribing to the MQTT topics and the device monitor will be configured to display all MQTT messages sent to each topic - effectively it is showing the list messages received and sent by Mosquitto.

With the IoT Agent connected via MQTT, the service group has defined the topic which the agent is subscribed to. Since the api-key matches the root of the topic, the MQTT message from the Motion Sensor is passed to the IoT Agent which has previously subscribed.

Because we have specifically provisioned the device (motion001) - the IoT Agent is able to map attributes before raising a request with the Orion Context Broker.

You can see that a measurement has been recorded by retrieving the entity data from the context broker. Don't forget to add the fiware-service and fiware-service-path headers.

5️⃣ Request:

curl -X GET \
  'http://localhost:1026/v2/entities/urn:ngsi-ld:Motion:001?type=Motion' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /'

Response:

{
    "id": "urn:ngsi-ld:Motion:001",
    "type": "Motion",
    "TimeInstant": {
        "type": "ISO8601",
        "value": "2018-05-25T10:51:32.00Z",
        "metadata": {}
    },
    "count": {
        "type": "Integer",
        "value": "1",
        "metadata": {
            "TimeInstant": {
                "type": "ISO8601",
                "value": "2018-05-25T10:51:32.646Z"
            }
        }
    }
}

The response shows that the Motion Sensor device with id=motion001 has been successfully identified by the IoT Agent and mapped to the entity id=urn:ngsi-ld:Motion:001. This new entity has been created within the context data. The c attribute from the dummy device measurement request has been mapped to the more meaningful count attribute within the context. As you will notice, a TimeInstant attribute has been added to both the entity and the metadata of the attribute - this represents the last time the entity and attribute have been updated, and is automatically added to each new entity because the IOTA_TIMESTAMP environment variable was set when the IoT Agent was started up.

Provisioning an Actuator

Provisioning an actuator is similar to provisioning a sensor. The transport=MQTT attribute defines the communications protocol to be used. For MQTT communications, the endpoint attribute is not required as there is no HTTP URL where the device is listening for commands. The array of commands is mapped to directly to messages sent to the /<api-key>/<device-id>/cmd topic The commands array includes a list of each command that can be invoked.

The example below provisions a bell with the deviceId=bell001.

6️⃣ Request:

curl -iX POST \
  'http://localhost:4041/iot/devices' \
  -H 'Content-Type: application/json' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /' \
  -d '{
  "devices": [
    {
      "device_id": "bell001",
      "entity_name": "urn:ngsi-ld:Bell:001",
      "entity_type": "Bell",
      "protocol": "PDI-IoTA-UltraLight",
      "transport": "MQTT",
      "commands": [
        { "name": "ring", "type": "command" }
       ],
       "static_attributes": [
         {"name":"refStore", "type": "Relationship","value": "urn:ngsi-ld:Store:001"}
      ]
    }
  ]
}
'

Before we wire-up the context broker, we can test that a command can be sent from the IoT Agent to a device by making a REST request directly to the IoT Agent's North Port using the /v2/op/update endpoint. It is this endpoint that will eventually be invoked by the context broker once we have connected it up. To test the configuration you can run the command directly as shown:

7️⃣ Request:

curl -iX POST \
  http://localhost:4041/v2/op/update \
  -H 'Content-Type: application/json' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /' \
  -d '{
    "actionType": "update",
    "entities": [
        {
            "type": "Bell",
            "id": "urn:ngsi-ld:Bell:001",
            "ring" : {
                "type": "command",
                "value": ""
            }
        }
    ]
}'

If you are viewing the device monitor page, you can also see the state of the bell change.

The result of the command to ring the bell can be read by querying the entity within the Orion Context Broker.

8️⃣ Request:

curl -X GET \
  'http://localhost:1026/v2/entities/urn:ngsi-ld:Bell:001?type=Bell&options=keyValues' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /'

Response:

{
    "id": "urn:ngsi-ld:Bell:001",
    "type": "Bell",
    "TimeInstant": "2018-05-25T20:06:28.00Z",
    "refStore": "urn:ngsi-ld:Store:001",
    "ring_info": " ring OK",
    "ring_status": "OK",
    "ring": ""
}

The TimeInstant shows last the time any command associated with the entity has been invoked. The result of ring command can be seen in the value of the ring_info attribute.

Provisioning a Smart Door

Provisioning a device which offers both commands and measurements is merely a matter of making an HTTP POST request with both attributes and command attributes in the body of the request. Once again the transport=MQTT attribute defines the communications protocol to be used, and no endpoint attribute is required as there is no HTTP URL where the device is listening for commands.

9️⃣ Request:

curl -iX POST \
  'http://localhost:4041/iot/devices' \
  -H 'Content-Type: application/json' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /' \
  -d '{
  "devices": [
    {
      "device_id": "door001",
      "entity_name": "urn:ngsi-ld:Door:001",
      "entity_type": "Door",
      "protocol": "PDI-IoTA-UltraLight",
      "transport": "MQTT",
      "commands": [
        {"name": "unlock","type": "command"},
        {"name": "open","type": "command"},
        {"name": "close","type": "command"},
        {"name": "lock","type": "command"}
       ],
       "attributes": [
        {"object_id": "s", "name": "state", "type":"Text"}
       ],
       "static_attributes": [
         {"name":"refStore", "type": "Relationship","value": "urn:ngsi-ld:Store:001"}
       ]
    }
  ]
}
'

Provisioning a Smart Lamp

Similarly, a Smart Lamp with two commands (on and off) and two attributes can be provisioned as follows:

1️⃣0️⃣ Request:

curl -iX POST \
  'http://localhost:4041/iot/devices' \
  -H 'Content-Type: application/json' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /' \
  -d '{
  "devices": [
    {
      "device_id": "lamp001",
      "entity_name": "urn:ngsi-ld:Lamp:001",
      "entity_type": "Lamp",
      "protocol": "PDI-IoTA-UltraLight",
      "transport": "MQTT",
      "commands": [
        {"name": "on","type": "command"},
        {"name": "off","type": "command"}
       ],
       "attributes": [
        {"object_id": "s", "name": "state", "type":"Text"},
        {"object_id": "l", "name": "luminosity", "type":"Integer"}
       ],
       "static_attributes": [
         {"name":"refStore", "type": "Relationship","value": "urn:ngsi-ld:Store:001"}
      ]
    }
  ]
}
'

The full list of provisioned devices can be obtained by making a GET request to the /iot/devices endpoint.

1️⃣1️⃣ Request:

curl -X GET \
  'http://localhost:4041/iot/devices' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /'

Enabling Context Broker Commands

Having connected up the IoT Agent to the IoT devices, the Orion Context Broker was informed that the commands now are available. In other words the IoT Agent registered itself as a Context Provider for the command attributes.

Once the commands have been registered it will be possible to ring the Bell, open and close the Smart Door and switch the Smart Lamp on and off by sending requests to the Orion Context Broker, rather than sending UltraLight 2.0 requests directly the IoT devices as we did in the previous tutorial

All the communications leaving and arriving at the North port of the IoT Agent use the standard NGSI syntax. The transport protocol used between the IoT devices and the IoT Agent is irrelevant to this layer of communication. Effectively the IoT Agent is offering a simplified facade pattern of well-known endpoints to actuate any device.

Therefore this section of registering and invoking commands duplicates the instructions found in the previous tutorial

Ringing the Bell

To invoke the ring command, the ring attribute must be updated in the context.

1️⃣2️⃣ Request:

curl -iX PATCH \
  'http://localhost:1026/v2/entities/urn:ngsi-ld:Bell:001/attrs' \
  -H 'Content-Type: application/json' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /' \
  -d '{
  "ring": {
      "type" : "command",
      "value" : ""
  }
}'

If you are viewing the device monitor page, you can also see the state of the bell change.

Opening the Smart Door

To invoke the open command, the open attribute must be updated in the context.

1️⃣3️⃣ Request:

curl -iX PATCH \
  'http://localhost:1026/v2/entities/urn:ngsi-ld:Door:001/attrs' \
  -H 'Content-Type: application/json' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /' \
  -d '{
  "open": {
      "type" : "command",
      "value" : ""
  }
}'

Switching on the Smart Lamp

To switch on the Smart Lamp, the on attribute must be updated in the context.

1️⃣4️⃣ Request:

curl -iX PATCH \
  'http://localhost:1026/v2/entities/urn:ngsi-ld:Lamp:001/attrs' \
  -H 'Content-Type: application/json' \
  -H 'fiware-service: openiot' \
  -H 'fiware-servicepath: /' \
  -d '{
  "on": {
      "type" : "command",
      "value" : ""
  }
}'

Next Steps

Want to learn how to add more complexity to your application by adding advanced features? You can find out by reading the other tutorials in this series

License

MIT © 2018-2020 FIWARE Foundation e.V.

Footnotes

  • Wikipedia: MQTT - a central communication point (known as the MQTT broker) which is in charge of dispatching all messages between services

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📙 FIWARE 203: Provisioning Ultralight with an alternative transport: IoT over MQTT

fiware-iotagent-ul.rtfd.io

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