The DataSetMessage header structure and the relation to other parts in a NetworkMessage is shown in Figure 29.
Figure 29 – DataSetMessage Header Structure
The encoding of the DataSetMessage header structure is specified in Table 81.
The DataSetFieldContentMask and the DataSetMessageContentMask settings of the DataSetWriter control the flags in the fields DataSetFlags1 and DataSetFlags2. The setting of the flags shall not change until the configuration of the DataSetWriter is changed.
Table 81 – DataSetMessage Header Structure
|
Name |
Type |
Description |
|
DataSetFlags1 |
Byte |
Bit 0: DataSetMessage is valid. If this bit is set to false, the rest of this DataSetMessage is considered invalid, and shall not be processed by the Subscriber. Bit range 1-2: Field Encoding 00 The DataSet fields are encoded as Variant The Variant can contain a StatusCode instead of the expected DataType if the status of the field is Bad. The Variant can contain a DataValue with the value and the statusCode if the status of the field is Uncertain. 01 RawData Field Encoding The DataSet fields are encoded in the DataTypes specified in the DataSetMetaData for the DataSet. The encoding is handled like a Structure DataType where the DataSet fields are handled like Structure fields and fields with Structure DataType are handled like nested structures. All restrictions for the encoding of Structure DataTypes also apply to the RawData Field Encoding. 10 DataValue Field Encoding The DataSet fields are encoded as DataValue. This option is set if the DataSet is configured to send more than the Value. 11 Reserved Bit 3: DataSetMessageSequenceNumber enabled Bit 4: Status enabled Bit 5: ConfigurationVersionMajorVersion enabled Bit 6: ConfigurationVersionMinorVersion enabled Bit 7: DataSetFlags2 enabled The bit shall be false, if DataSetFlags2 is 0. |
|
DataSetFlags2 |
Byte |
The DataSetFlags2 shall be omitted if bit 7 of the DataSetFlags1 is false. If the field is omitted, the Subscriber shall handle the related bits as false. Bit range 0-3: UADP DataSetMessage type 0000Data Key Frame (see 7.2.2.3.5) If the DataSetFlags2 field is not provided, this is the default DataSetMessage type. 0001Data Delta Frame (see 7.2.2.3.6) 0010Event (see 7.2.2.3.7) 0011Keep Alive (see 7.2.2.3.8) 01xxReserved 1xxxReserved Bit 4: Timestamp enabled Bit 5: PicoSeconds included in the DataSetMessage header Bit 6: Reserved Bit 7: Reserved for further extended flag fields |
|
DataSetMessageSequenceNumber |
UInt16 |
A strictly monotonically increasing sequence number assigned by the publisher to each DataSetMessage sent. A receiver should ignore older DataSetMessage than the last sequence processed if it does not handle reordering of DataSetMessages. Receivers need to be aware of sequence numbers roll over (change from 65535 to 0). To determine whether a received DataSetMessage is newer than the last processed DataSetMessage the following formula shall be used: (65535 + received sequence number – last processed sequence number) modulo 65536 Results below 16384 indicate that the received DataSetMessage is newer than the last processed DataSetMessage and the received DataSetMessage is processed. Results above 49162 indicate that the received message is older (or same) than the last processed DataSetMessage and the received DataSetMessage should be ignored if reordering of DataSetMessages is not necessary. Other results are invalid and the DataSetMessage shall be ignored. The field shall be omitted if Bit 2 of DataSetFlags1 is false. |
|
Timestamp |
UtcTime |
The time the Data was collected. The Timestamp shall be omitted if Bit 3 of DataSetFlags1 is false. |
|
PicoSeconds |
UInt16 |
Specifies the number of 10 picoseconds (1,0 e-11 seconds) intervals which shall be added to the Timestamp. The field shall be omitted if Bit 4 of DataSetFlags2 is false. |
|
Status |
UInt16 |
The overall status of the DataSet. This is the high order 16 bits of the StatusCode DataType representing the numeric value of the Severity and SubCode of the StatusCode DataType. The field shall be omitted if Bit 4 of DataSetFlags1 is false. |
|
ConfigurationVersion MajorVersion |
VersionTime |
The major version of the configuration version of the DataSet used as consistency check with the DataSetMetaData available on the Subscriber side. The field shall be omitted if Bit 5 of DataSetFlags1 is false. |
|
ConfigurationVersion MinorVersion |
VersionTime |
The minor version of the configuration version of the DataSet used as consistency check with the DataSetMetaData available on the Subscriber side. The field shall be omitted if Bit 6 of DataSetFlags1 is false. |