- Each domain controller tracks changes with Update Sequence Numbers (USN)
- USNs are unique to the domain controller, each DC tracks USNs itself
- USNs are unique, each change increments the USN
- AD objects have a uSNChanged and uSNCreated attribute
- When a change is committed to AD the USN number for the transaction is recorded to the AD object
- Sync to cache
- Pull changes to HRS
- Pull changes to application