• Microsoft Identity Integration Server—In order to synchronize data across your forests, you must deploy Microsoft Identity Integration Server (MIIS). The following QFE is required for proper cross-forest synchronization: Update for Microsoft Identity Intergration Server 2003 http://go.microsoft.com/fwlink/?LinkID=149029 . For information about how to deploy Identity Integration Server, see the Identity Integration Server documentation.
  
  
• Office Communications Server deployed in your central forest—If you have not deployed Office Communications Server, see the Microsoft Office Communications Server 2007 R2 Planning and Architecture documentation and the Microsoft Office Communications Server 2007 R2 Deployment documentation.
  
  

The central forest can be an existing forest that hosts existing Office Communications Server servers, users, groups, contacts, or you can create an entirely new forest.

The central forest should normally be the one that hosts the largest number of users. Connectivity between the central forest and other forests should also be highly available. Figure 1 shows how an example organization, Contoso, configured an Enterprise pool in its central forest.

Figure 1. Example of a Multiple Forest topology

After you have deployed Communications Server in the central forest, complete the following steps:

• Step 1: Configure MIIS for Office Communications Server 2007 R2
  
  
• Step 2: Enable Contacts for Office Communications Server 2007 R2