Estimate AD replication traffic per cycle, site link utilisation and end-to-end convergence time.
The KCC builds a bidirectional ring within a site, so a change travels at most half the ring to reach every controller, one replication interval per hop. Traffic per cycle is the change volume in the window, compressed for inter-site links. Convergence time, not bandwidth, is usually the constraint: with a 15-minute interval and twelve controllers a password change can take an hour and a half to be visible everywhere.
Active Directory Replication
bytes per cycle = changes per hour × interval ÷ 60 × bytes per object ÷ compression ratio.
Ring topology convergence
convergence = ceil(DCs ÷ 2) × replication interval
bytes per cycle = changes per hour × interval ÷ 60 × bytes per object ÷ compression ratio. The KCC builds a bidirectional ring within a site, so a change travels at most half the ring to reach every controller, one replication interval per hop. Traffic per cycle is the change volume in the window, compressed for inter-site links.
Convergence time, not bandwidth, is usually the constraint: with a 15-minute interval and twelve controllers a password change can take an hour and a half to be visible everywhere.
This calculator takes 6 inputs: Domain controllers, Directory changes per hour, Bytes per changed object, Replication interval, Site link bandwidth, Inter-site compression ratio. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.