I ran into a poster that Microsoft published a few days ago that details the traffic flow of protocols and ports used in each workload within Office Communications Server 2007 R2 (OCS 2007 R2). OCS 2007 R2 supports the following workloads: IM and Presence, Conferencing, Application Sharing, and Enterprise Voice. These filtered views can assist you in architecting your deployment of Communications Server 2007 R2. The different server roles are described along with server certificate requirements. Firewall and DNS configuration requirements are also described.