Source: Real-Time Innovations ( Gerardo Pardo-Castellote)
The GAP message indicates a gap in sequence numbers that is "not available" to the DataReader. It may be caused by filters (time, content), history keep last, or lifespan.
In some cases the reason behind the gap is important to the receiving application. For example a missing sequence number caused by a writer-side content filter does not invalidate a coherent change. However if the gap is caused by keep-last history the coherent change must be discarded by the subscriber/reader.
Currently there is no way for the receiving application to tell the difference.
There may be also other situations where it may be desirable to account for the different reasons that cause a gap. For example if the reader maintains a "sample lost count" it needs some way to distinguish sample loss from things it it chose to not receive.
The RTF should address this issue and provide the means to discriminate these cases. A possible approach would be include the information in the flags of the GAP message.
Reported: DDSI-RTPS 2.3b1 — Thu, 28 Feb 2019 02:41 GMT
Updated: Thu, 28 Feb 2019 02:41 GMT