Siemens SIMATIC S7-1500 Function Manual page 242

Subscription states and state transitions
①
②
③
④
⑤
⑥
⑦
Figure 9-50
Description of the subscription states
A subscription in the OPC UA server can have the following states:
Status
Creating
Normal
Closed
KeepAlive
Late
TimedOut
Communication
Function Manual, 11/2019, A5E03735815-AH
Subscription is generated and is then active.
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.
See explanation in table for "Late"; for example, no requests to send from client.
Maximum KeepAlive value reached.
See explanation in table for "TimedOut".
Maximum lifetime of subscription reached.
Client has deleted subscription.
Subscription states and state transitions
Meaning
Client has requested a subscription in the server; the server creates the sub-
scription.
Subscription is created in the server and active.
Client has deleted the subscription.
Status if the monitored items do not change over a long period of time. These
state transitions are not entered in the diagnostic buffer.
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).
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.
OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
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