The Action execution sequence and the related ActionMetaData for an Action execution through a reliable transport protocol like MQTT is described in Figure 26.
Figure 26 – Action execution sequence reliable transport
The RequestId is unique within the context of a RequestorId and CorrelationData. Each Action request in a single NetworkMessage has a different RequestId. Multiple NetworkMessages with the same RequestorId and CorrelationData may be sent.
Multiple Responses may be sent in the same NetworkMessage if the corresponding requests have the same RequestorId and CorrelationData. The grouping of requests in NetworkMessages does not affect the grouping of Responses into NetworkMessages.
The Action execution sequence for an Action execution through a non-reliable transport protocol like UDP is described in Figure 27. The related ActionMetaData is described in Figure 26. It shows the use of the ActionState for a non-reliable transport protocol. The request and response messages are send in the PublishingInterval of the Responder as long as the ActionState requires the exchange of messages for a Action execution.
The state changes for Action execution are defined in Table 82 for the Requestor and in Table 83 for the Responder.
Table 82 – Action execution state changes Requestor
|
Current State |
Condition |
Event |
State for next message |
|
Idle |
Start Action execution |
Requestor sends Request Message with ActionState = Executing. |
Executing |
|
Executing |
PublishingInterval expired and no Done or Executing received from Responder. |
Requestor sends Request Message again with ActionState = Executing. |
Executing |
|
Executing |
Received Done from Responder |
Requestor sends Request Message with ActionState = Idle |
Idle |
|
Done |
PublisihingInterval expire and no Idle received. |
Requestor sends Request Message again with ActionState = Idle. |
Idle |
|
Done |
Received Idle from Responder |
None |
|
Table 83 – Action execution state changes Responder
|
Current State |
Condition |
Event |
State for next message |
|
Idle |
Receives RequestMessage for a new combination of RequestorId, CorrelationData and RequestId. |
Begins processing Action. |
Executing |
|
Executing |
PublshingInterval expired and Action execution is still in progress. |
Responder sends Response Message with ActionState = Executing, Status = Good and the payload is empty. |
Executing |
|
Executing |
Action execution completed. |
Responder sends Response Message with ActionState = Done, Status = Action result and payload provided for Good and Uncertain Status and payload is empty for Bad Status. |
Done |
|
Done |
PublshingInterval expired and did not receive Idle from Requestor yet |
Responder sends Response Message again with ActionState = Done until Idle is received from the Requestor or the time duration defined by the TimeoutHint request parameter ends. |
Done |
|
Done |
Received Idle from Requestor |
None |
|
Figure 27 – Action execution sequence non-reliable transport
Errors during the execution of an Action are reported in the Status of the Action response message.
For some errors such as decoding errors for the request message, addressing errors or failing security checks, the Responder does not produce a response message. Therefore the Requestor should have an internal timeout setting to stop waiting for a response message.