I often get asked questions around recommended architectures for OCS, as well as what is supported and what is not.
The best place to start for this information is the OCS Supportability Guide. This document is a great resource for information on what are the network/infrastructure requirements for OCS, as well as supported topologies/architectures.
The purpose of the Microsoft Office Communications Server 2007 Supportability Guide is to provide a central, high-level reference for supported Office Communications Server 2007 topologies and configurations. It is also intended to answer frequently asked questions. This document identifies supported topologies, configurations, and scenarios described in detail in the existing deployment and planning documentation.