In a branch office, a single domain or single-master domain can usually be used. Companies with many small branch offices can group branch offices together into regional domains that will provide administration for the branches.
When the branch office is linked to the PDC by means of a communications link or modem, a BDC would be the on-site server. The BDC handles local authentication and local file and print services. A second BDC can be added for fault tolerance.
Figure 2.7 Branch Offices domain model