Settings Of The Server For Subscriptions - Siemens SIMATIC ET 200AL System Manual

OPC UA communication
9.3 Using the S7-1500 as an OPC UA server
Backward compatible data type definitions according to OPC UA specification ≤ V1.03
The OPC UA specification (<= V1.03) defines mechanisms in order to read out data type
definitions, for example for user-defined structures (UDTs), from a server by means of the
TypeDictionaries.
In the OPC UA server properties of the CPU, you can set whether the CPU generates these
backward compatible data type definitions according to the OPC UA specification ≤ V1.03 for
the standard SIMATIC server interface or not.
Because TypeDictionaries are complex and result in large OPC UA XML files (server interfaces)
which the client has to interpret, a simpler solution was introduced with OPC UA Specification
V1.04 (attribute "DataTypeDefinition" at the data type node). If your client supports the OPC
UA specification V1.04 or higher, then disable the option.
Advantages of the data type definitions according to OPC UA specification as of V1.04:
• The server starts faster
• The memory is used more efficiently
• The "Browse" function is faster
9.3.3.4

Settings of the server for subscriptions

Subscription instead of cyclic queries
An alternative to cyclic queries for a PLC tag (polling) is to monitor this value. Use a
Subscription: The server informs the client if the value of PLC tags changes. See "The OPC UA
client".
One server usually monitors a large number of PLC values. For this reason, the server sends
notifications to the client at regular intervals containing the new values of the PLC tags.
Advantages of subscriptions:
• The server starts faster
• The memory is used efficiently
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Function Manual, 05/2021, A5E03735815-AJ
Communication