The parameter NetworkMessageNumber with the DataType UInt16 is the number of the NetworkMessage inside a PublishingInterval in which this DataSetMessage is published. The default value is 0 and indicates that the number of the NetworkMessage is not fixed.
The NetworkMessage shall have a fixed layout if the PayloadHeader flag in the NetworkMessageContentMask is false.
If the NetworkMessage layout is fixed and all DataSetMessages of a WriterGroup fit into one single NetworkMessage, the value of NetworkMessageNumber shall be 1. If the DataSetMessages of a WriterGroup are distributed or chunked over more than one NetworkMessage, the first NetworkMessage in a PublishingInterval shall be generated with the value 1, the following NetworkMessages shall be generated with incrementing NetworkMessageNumbers. To avoid a roll-over the number of NetworkMessages generated from one WriterGroup within one PublishingInterval is limited to 65535.