The parameter NetworkMessageNumber with the DataType UInt16 is a read-only parameter set by the Publisher in the case of a fixed NetworkMessage layout. The default value is 0 and indicates that the position of the DataSetMessage in a NetworkMessage is not fixed.
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.