Annex C (normative) UADP Header Layouts ToC

C.2 Message headers for periodic data with fixed layout ToC Previous Next

C.2.8 Examples ToC Previous Next

C.2.8.1 Fixed message layout without security ToC

Figure C.5 shows an example for a UADP NetworkMessage with fixed layout as defined in C.2.3 and 0.

The configuration ensures that every NetworkMessage sent has the same layout of header fields and also the same layout of DataSetFields. This allows a highly efficient encoding and decoding of the message because the offset of all fields is constant and can be precalculated. The Payload Header (Count and Sizes for the DataSetMessages and DataSetWriterIds) is deactivated and the Subscriber has to retrieve this information through the DataSetMetaData, DataSetWriter and WriterGroup settings.

The configuration has to ensure that the size of each DataSetMessage is constant. This can be achieved by avoiding DataSetFields of types with variable size, or by using the parameter ConfiguredSize. In this example it is assumed that DataSetMessage[1] and DataSetMessage[W-1] are using RawData field encoding and all DataSet fields are from constant size, so the total length of theses DataSetMessages can be calculated from the DataSetMetaData. For DataSetMessage[0] in this example the Subscriber does not have to calculate the total length but it should take it from the parameter ConfiguredSize. This allows to provide spare bytes for future extension of DataSetMessage[0] without effect on the size of the complete NetworkMessage or the position of other DataSetMessages in this NetworkMessage.

By setting specific values for KeyFrameCount and DataSetOrdering (see Table C.6) it is guaranteed that the number of DataSetMessages and their order inside the NetworkMessage is the same in every NetworkMessage that is sent.

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Figure C.5 : Example for fixed message layout without security

C.2.8.2 Fixed message layout with integrity ToC

Figure C.6 shows an example for a UADP NetworkMessage with fixed layout and security activated (signing, no encryption) as defined in C.2.5 and 0.

The layout of all header fields and DataSet fields is constant like described in C.2.8.1. Additional to this the SecurityHeader is activated for signing (but no encryption).

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Figure C.6 : Example for fixed message layout without signature

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