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Open Mobile Alliance (OMA) - Next Generation Services Interface (NGSI)

The ngsi node type implements an interface to FIWARE context brokers. Currently version 1 of the RESTful HTTP API is implemented and using NGSI10 for the context management interface.

This implementation if currently limited to the updateContext operation. Therefore only publishing updates is supported. Subscription or polling of events is planned for later versions.

Prerequisites​

This node-type requires to following libraries to communicate with the context broker over JSON:

Implementation​

The source code of the node-type is available here: https://github.com/VILLASframework/node/blob/master/lib/nodes/ngsi.cpp

Configuration​

You can use the vectorize setting to send multiple samples in a vector.

Every ngsi node supports the following special settings:

endpoint
required
string <uri>
entity_id
string

ID of NGSI entity.

entity_type
string

Type of NGSI entity.

ssl_verify
boolean

Verify SSL certificate against local trust store.

timeout
number
Default: 1

Timeout in seconds for HTTP requests.

rate
number
Default: 1

Polling rate in Hz for requesting entity updates from broker.

access_token
string

Send 'Auth-Token' header with every HTTP request.

create
boolean
Default: true

Create NGSI entities during startup of node.

object (Input configuration (received by VILLASnode))
vectorize
integer
Default: 1

This setting allows to send multiple samples in a single message to the destination nodes.

The value of this setting determines how many samples will be combined into one packet.

Array of Hook Object (object) or Hook Name (string) (hook_list)
builtin
boolean (Builtin hook functions)
Default: true

By default, each node and paths has a couple of default hooks attached to them. With this setting the attachment of built-in hooks can be disabled.

object (Output configuration (sent out by VILLASnode))
{
  • "endpoint": "http://example.com",
  • "entity_id": "string",
  • "entity_type": "string",
  • "ssl_verify": true,
  • "timeout": 1,
  • "rate": 1,
  • "access_token": "string",
  • "create": true,
  • "in": {
    },
  • "vectorize": 1,
  • "hooks": [
    ],
  • "builtin": true,
  • "out": {
    }
}

Example​

node/etc/examples/nodes/ngsi.conf
nodes = {
    ngsi_node = {
        type = "ngsi"

        # The HTTP REST API endpoint of the FIRWARE context broker
        endpoint = "http://46.101.131.212:1026"

        # Add an 'Auth-Token' token header to each request
        access_token = "aig1aaQuohsh5pee9uiC2Bae3loSh9wu"

        entity_id = "S3_ElectricalGrid"
        entity_type = "ElectricalGridMonitoring"

        # Create the NGSI entities during startup
        create = true

        # Rate at which we poll the broker for updates
        rate = 0.1

        # Timeout of HTTP request in seconds (default is 1, must be smaller than 1 / rate)
        timeout = 1

        # Verification of SSL server certificates (default is true)
        verify_ssl = false

        in = {
            signals = (
                {
                    name = "attr1"
                    ngsi_attribute_name = "attr1" # Defaults to signal 'name'
                    ngsi_attribute_type = "Volts" # Default to signal 'unit'
                    ngsi_attribute_metadatas = (
                        { name="accuracy", type="percent", value="5" }
                    )
                }
            )
        }

        out = {
            signals = (
                { name="PTotalLosses", unit="MW" },
                { name="QTotalLosses", unit="Mvar" }
            )
        }
    }
}

Further reading​

This standard was specified by the Open Mobile Alliance (OMA).