A.2.2 Message headers for Events and Data with dynamic layout

A.2.2.1 Motivation

In PubSub use cases with dynamically changing message layouts or Event based DataSetMessages, the number and ordering of DataSetMessages within different NetworkMessages can change arbitrarily. The header layouts described in this section are intended for use cases with dynamic DataSets and ad-hoc identification of DataSetMessages.

A.2.2.2 Overview

With the header layout described in this section, the NetworkMessage header only identifies the Publisher and the contained DataSetMessages. In contrast to the fixed layout, more header fields are enabled in the DataSetMessage header with this header layout but the GroupHeader is deactivated.

A.2.2.3 Header layout URI

The header layout URI for the dynamic layout as specified in A.2.2.4, A.2.2.5, A.2.2.6 and A.2.2.7 is

A.2.2.4 Header layout for NetworkMessages

A UADP NetworkMessage header shall consist of the following fields according to this header layout:

Version/Flags

ExtendedFlags1

PublisherId

PayloadHeader

Additional restrictions:

The datatype for the PublisherId shall be UInt64

The NetworkMessage header layout is shown in Figure A.7.

Table A.7 shows the configuration for the NetworkMessage header.

Table A.8 defines the values for the configuration parameters representing this layout.

When a PubSubConnection is created by using the Method AddConnection() the element PublisherId contained in the argument PubSubConnectionDataType shall be of the DataType UInt64.

A.2.2.5 Header layout for NetworkMessages with integrity (signing)

UADP messages may be signed to ensure integrity. In this case a security header and a signature have to be added to the message. See clause 7.2.4.4.3 for a complete description of the signing mechanism.

This header layout is basically the same as the header layout defined in A.2.2.4 but with additional security level ‘Signing but no encryption’. The NetworkMessage header layout with signing is shown in Figure A.8.

Table A.9 shows the configuration for the NetworkMessage header with signing. The table contains only the added or modified rows from Table A.7.

A.2.2.6 Header layout for NetworkMessages with integrity and confidentiality (signing and encryption)

UADP messages may be signed and encrypted. In this case the SecurityHeader and the Signature have to be added to the message. See clause 7.2.4.4.3 for a complete description of the security mechanisms.

This header layout is basically the same as the header layout defined in A.2.2.4 but with additional security level ‘Signing and encryption’. The NetworkMessage header layout with signing and encryption is shown in Figure A.9.

Table A.10 shows the configuration for the NetworkMessage header with signing and encryption. The table contains only the added or modified rows from Table A.7.

A.2.2.7 Header layout for DataSetMessages

A UADP DataSetMessage header shall consist of the following fields according to this header layout:

DataSetFlags1

DataSetFlags2

DataSetMessageSequenceNumber

Timestamp

Status

MinorVersion

Additional remarks:

Fields can use any encoding

All types of DataSetMessages (Data Key Frame, Data Delta Frame, Event, etc.) are supported

The DataSetMessage header layout is shown in Figure A.10

Table A.11 shows the configuration for the DataSetMessage header.

Table A.12 defines the values for the configuration parameters representing this layout.

A.2.2.8 Example dynamic message layout with different DataSetMessage types

Figure A.11 shows an example for a UADP NetworkMessage with dynamic layout. As defined in A.2.2.3 and A.2.2.7 only the layout of the NetworkMessage header and the DataSetMessage header is fixed. The number, the type, the length, and the order of DataSetMessages can vary from one NetworkMessage to the next.