Fast forward

A node will "fast forward" when it has a complete account tree which is synced to some point in the past by applying all the transactions missed by the node while it was offline. If the node has been offline longer than the cycle time then fast forwarding might not be possible and the node will have to do a full resync. When a new node first synchronizes with the network it will attempt to build an old account tree which would have existed a cycle ago and then it will fast forward the tree to a state matching the latest master hash.