Siemens SIMATIC ET 200AL, System Manual

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OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
Communication
312
Function Manual, 05/2021, A5E03735815-AJ
Subscription states and state transitions
① Subscription is generated and is then active.
② Status change is not entered in the diagnostic buffer because too many entries may be made in
the diagnostic buffer depending on the amount of data.
③ See explanation in table for "Late"; for example, no requests to send from client.
④ Maximum KeepAlive value reached.
⑤ See explanation in table for "TimedOut".
⑥ Maximum lifetime of subscription reached.
⑦ Client has deleted subscription.
Figure 9-54 Subscription states and state transitions
Description of the subscription states
A subscription in the OPC UA server can have the following states:
Status Meaning
Creating Client has requested a subscription in the server; the server creates the subscrip-
tion.
Normal Subscription is created in the server and active.
Closed Client has deleted the subscription.
KeepAlive Status if the monitored items do not change over a long period of time. These
state transitions are not entered in the diagnostic buffer.
Late Client has generated a subscription with minimal sampling and publishing inter-
vals. The amount of monitored items is not transmitted to the client during this
time.
Client no longer transmits requests to send (for example, due to failure).
TimedOut The client has requested a subscription.
The server can only honor the subscription (send Publish Response) when there is
a sufficient number of send requests (Publish Requests) from the client.
When the client stops sending subscription requests, the subscription enters the
"TimedOut" state after a certain time.
Subscription: Error in the sampling times
As of firmware V2.5 of the SIMATIC S7-1500 CPU, the OPC UA server can transmit the status
code "GoodOverload" when using subscriptions, if an overload of the CPU occurs when
sampling the items.
As of firmware V2.8 of the SIMATIC S7-1500 CPU, the OPC UA server can also enter this event
into the diagnostic buffer.