Imported from previous forum
After After FIX session has been interrupted and at the time of re-connecting there is a chance for ambiguity.
- One of the parties may re-request some data that was previously sent (due to request from a trading system).
- At the same time the other party may changed the sequence numbers to be lower than before a disconnect occurred.
If the party that lowers sequence numbers stays with a sequence number higher than what has been re-requested (by resend request), then an error (lower sequence number) will not be detected.
This is an issue with all protocols that are based on push and pull mechanism (or mutual trust) where both parties engaged in a session have mutual responsibility to provide guaranteed message delivery within one day.