Observations
Observation definition
An Observation allows Live Objects to be notified when some Attributes change on the device. It can target:
-
a specific Attribute
-
an Object Instance
-
all Object Instances of an Object
-
several Attributes (Observation Composite)
Example of an Observation targeting an Object Instance:
{
"id": "631f1190d4135d0066541e8b",
"paths": [
"/6/0"
],
"status": "PENDING",
"name": "Observation on the location Object",
"created": "2022-09-12T11:02:29.811Z"
}| Field | Example | Comment |
|---|---|---|
id |
|
Observation unique id, generated by Live Objects |
paths |
|
Target paths of related device objects or attributes to observe |
status |
|
Current status of the Observation among |
name |
|
User-defined name for the Observation |
created |
|
Observation creation date |
Observation Lifecycle
An Observation is created using the API and its status will be available via the API too.
Once created, the Observation is sent immediately if the device is ONLINE or the next time the device sends an Update or Register otherwise.
Depending on the type of error, Observations that have failed can be automatically re-sent at the next Update. The number of attempts is nevertheless limited.
When a LwM2M device goes offline (de-registration or the lifetime of the registration expires), the Observations on Live Objects for this device go back to the PENDING state. They will be automatically re-sent when the device sends a Register, regardless of their status.
An Observation can be cancelled. Upon the user cancellation request, a Cancel Observation operation is sent to the device if it is ONLINE. Otherwise, the cancellation occurs at the next Notify.
| status | Comment |
|---|---|
PENDING |
The Observation has been created and is ready to be sent. |
FAILED |
The Observation has not succeeded after the maximum number of attempts. |
OBSERVING |
The Observation is active on the device. |
Observation retry policy
For errors that are considered as unrecoverable, there will be only one attempt to send an Observation. The following errors fall in this category:
-
The device responded with a 4xx code
-
The device rejected the request
For other errors there will be 5 attempts. For instance, we can mention a 5xx response or a time-out.
Observation configuration
The parameters related to an Observation can be configured by the Write-Metadata operation.
Observation limits
The number of Observations per device is limited regardless of their status.