data on wire general question

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data on wire general question

Hello, I am still building my understanding of DDS- RTPS 2.1 data.

My understanding is that the first part of the datagram is going to be the Message header.

Directly after that will be the first sub-message header which will have the ID byte, Flags Byte and 2 sub-message length bytes.

So

ID will always be a hex value 0x01 to 0xFF

Flags will always be 0x00 to 0xFF??

Length I guess could be 0x0000 but probably not? ____(can it?)

Can the ID might be zeroed?

If the sub-message length is zero that means that it would be directly followed by another sub-message or the end of the datagram Correct?

The next point of confusion I wanted to clarify in my mind is value of "a standard practice" of looking at a single sub-message out side of the other sub-messages. From the OMG standard its my understanding that the previous sub-messages can affect the meaning of subsequent ones - therefore, you need all of them to make sure you are ALWAYS getting the correct meaning in the sub-messages. Correct?

Thank you

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