In a central forest topology, Microsoft Office Communications Server servers in the central forest provide services to users and groups in the central forest, as well as to users and groups in all other forests, which are called user forests.
The central forest deployment offers the benefits of centralized administration and minimizes complexity in a multiple forest environment.
Part 1 of this document explains how to configure Office Communications Server 2007 R2 to support users, groups, and distribution group expansion in a central forest environment. It briefly describes the multiple-forest environment, but it assumes that you have already deployed the hardware and software so that you are ready to create and propagate user data so that a user in any forest can connect to Office Communications Server and communicate with any user in any connected forest.