The data delta frame DataSetMessage data and the related headers are shown in Figure 33.
Figure 33 – Data Delta Frame DataSetMessage
The information for a single value in delta frame messages is larger because of the additional index necessary for sending just changed data. The Publisher shall send a key frame message if the delta frame message is larger than a key frame message.
The encoding of the data delta frame DataSetMessage structure is specified in Table 147.
Table 147 – Data Delta Frame DataSetMessage structure
|
Name |
Type |
Description |
|
FieldCount |
UInt16 |
Number of fields of the DataSet contained in the DataSetMessage. |
|
DeltaFrameFields |
Structure [FieldCount] |
The subset of field values of the DataSet contained in the delta frame. |
|
FieldIndex |
UInt16 |
The index of the Field in the DataSet. The index is based on the field position in the DataSetMetaData with the configuration version defined in the ConfigurationVersion field. A Publisher shall use an index only once in a DataSetMessage. |
|
FieldValue |
BaseDataType |
The field values of the DataSet. The field encoding depends on the DataSetFlags1.Field Encoding of the DataSetMessage Header defined in 7.2.4.5.4. The default encoding is Variant if bit 1 and 2 are not set. |
|
Padding |
Byte [*] |
Optional padding added if the encoded DataSetMessage is smaller than the ConfiguredSize. The DataSetMessage is padded with bytes with value zero. |