Assumption of successful synchronization
The export and import phases of synchronization always occur at
different times. A sending replica does not require acknowledgment from a
sibling replica that a packet has been received and processed successfully.
Instead, the sending replica assumes success. This assumption enables an optimization:
subsequent updates from a replica do not include the data sent in previous
updates.
If a failure does occur (for example, a packet is lost in transit or a CD is unreadable at the sibling replica), you must adjust the epoch numbers at the sending replica to enable the lost data to be sent again.