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- If the MQTT server supports Topic aliases, use MQTT Version = MQTT 5.0, and set Topic Alias Maximum to a value greater than the number of stations on the line (for Payload Type = Sparkplug Edge Node) or greater than the number of topics expected from the MQTT broker (for Payload Type = Text only / JSON). On the MQTT broker side, ensure that its Topic Alias Maximum value is greater than the number of topics that will be sent to the D2000 KOM process, so that numeric aliases can be used instead of text topics.
Note: the Topic Alias Maximum value that the MQTT broker sends when connecting as a parameter of the CONNACK message is visible in the communication logs:
09:31:12.086 13-05-2025|D|MQTT> CONNACK Property # 1 Topic Alias Maximum ( 34)
09:31:12.087 13-05-2025|T|MQTT> Recv:<00><0A>
09:31:12.088 13-05-2025|D|MQTT> CONNACK Property value= 10 - Use aliases for metrics (for Payload Type = Sparkplug Edge Node): automatically using the Sparkplug Alias Mode=Automatic (HOBJ) parameter or manually using the SAL=alias item in the I/O tag address. If you use manual aliases, use low numbers (aliases 10-127 are encoded as 1 byte).
- For Payload Type = Sparkplug Edge Node: if there are many changes to the output I/O tags, we recommend setting the Batch Size parameter to a larger value than the default (10) and possibly increasing the Delay parameter in the station's time parameters. This will cause fewer messages to be generated (and each will contain multiple metrics), which reduces the overhead required to transmit one metric. If specific I/O tags change frequently, the message may contain several values for the same I/O tag (with timestamps). The disadvantage is the delay in the values.
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