SIA-Query and SIA-Reply are used when the diffusing computation takes a long amount of time to verify if a neighbor that has not yet sent a Reply to a Query is truly reachable and still participating in the diffusing computation.
The SIA-Query packet is used to ask a neighbor to confirm if they are still working on the original Query.
If the neighbor is still engaged in the diffusing computation and awaiting the original Reply, it sends a SIA-Reply to the originator of the SIA-Query.
This resets the timer that governs the max time alloted for the diffusing computation to complete.
SIA-Query is assigned Opcode of 10
SIA-Reply is assigned Opcode of 11