If a NetworkMessage payload with a DataSetMessage need to be split across multiple NetworkMessages, the chunks are sent in multiple NetworkMessages. The PayloadHeader of each NetworkMessage contains the payload header defined in Table 141. The Payload of each NetworkMessage contains the payload defined in Table 142. A chunk NetworkMessage can only contain chunked payload of one DataSetMessage.
If a NetworkMessage payload with a discovery announcement message has to be split across multiple NetworkMessages the chunks are sent with the payload defined in Table 142. The payload header is disabled for discovery probe and discovery announcement NetworkMessages.
Table 141 – Chunked NetworkMessage payload header
|
Name |
Type |
Description |
|
DataSetWriterId |
UInt16 |
DataSetWriterId contained in the NetworkMessage. The DataSetWriterId identifies the PublishedDataSet and the DataSetWriter responsible for sending Messages for the DataSet. A Subscriber can skip DataSetMessages from DataSetWriters it does not expect DataSetMessages from. |
Table 142 – Chunked NetworkMessage payload fields
|
Name |
Type |
Description |
|
MessageSequenceNumber |
UInt16 |
Sequence number of the payload as defined for the NetworkMessage type like DataSetMessageSequenceNumber in a DataSetMessage. NetworkMessages may be received out of order. In this case, a chunk for the next payload can be received before the last chunk of the previous payload was received. If the next sequence number is received by a Subscriber that can handle only one payload, the chunks of the previous payload are skipped if they are not completely received yet. |
|
ChunkOffset |
UInt32 |
The byte offset position of the chunk in the complete NetworkMessage payload. The last chunk is detected if ChunkOffset plus the size of the current chunk equals TotalSize. All chunks, except for the last one shall have the same size. The size of all chunks other than the last one can be used to calculate the number of expected chunks. The reassembled NetworkMessage payload can be processed after all chunks are received. Depending on the transport protocol mapping, the chunks may be received out of order and the last chunk may be received before all other chunks are received. |
|
TotalSize |
UInt32 |
Total size of the NetworkMessage payload in bytes. |
|
ChunkData |
ByteString |
The pieces of the original DataSetMessage or the discovery announcement message are copied into the chunk until the maximum size allowed for a single NetworkMessage is reached minus space for the signature. The data copied into next chunk starts with the byte after the last byte copied into current chunk. A DataSetMessage or discovery announcement message is completely received when all chunks are received and the message can be processed completely. |